One Community
Sustainable Roadways, Walkways, and Landscaping
This page is about the sustainable construction of roadways, walkways, and landscaping. We are committed to sustainable, ethical, durable, and affordable construction practices and researched these as part of our 7 open source sustainable village models. We discuss the results of this research in the following sections:
- What are Sustainable Roadways, Walkways, and Landscaping
- Why Open Source Sustainable Roadways, Walkways, and Landscaping
- Ways to Contribute and Consultants
- Sustainable Roadways, Walkways, and Landscaping Details
- Pavement Types
- Pavement Designs
- Process Overview
- Preparing a Pavement Recommendation
- Project Specific Conditions To Consider
- Roadways Drainage and Collections
- Fire Department Access
- Water Catchment
- Streetscape and Walkway Design
- Walkways
- Landscaping
- ADA Requirements
- Parking Lot Design Standards
- Handrail Design Standards
- Stairway Design
- Bicycle Design
- Road Design Specifics
- One Community’s Pavement and Walkways Plan (Case Study)
- Open Source Content Coming Later
- Resources
- Summary
- FAQ
- Glossary
RELATED PAGES (Click icons for complete pages)
WHAT ARE SUSTAINABLE ROADWAYS, WALKWAYS, AND LANDSCAPING?
According to Leadership in Energy and Environmental Design (LEED), sustainable infrastructure is structures and facilities that are highly efficient, ede high savings in energy and water, have efficient materials, are innovative, environmentally safe, and economically resourceful. For our roadways, walkways, and landscaping, One Community Global has set these standards as a minimum criterion and has also researched many resources to make our designs replicable, durable, and easy to build. This page offers a step-by-step tutorial that covers planning phase analysis, design considerations, design, costs, and operations & maintenance for the design of roadways, walkways, and landscaping elements of our project. We also go into detail and compare many different options of roadway, landscaping, and walkway materials to ensure that our design meets the highest level of sustainability possible. The design and research for this project follow the standards and requirements given in the San Diego Drainage Manual, AASHTO highway design manual, and Utah’s highway design manual. Please double-check with your local or state requirements to make sure that these requirements are sufficient for your site and location before moving forward with your design.
WHY OPEN SOURCE SUSTAINABLE ROADWAYS, WALKWAYS, AND LANDSCAPING?
These open source tutorials will be used as guides for when One Community begins to move forward with the construction and development of our roadways, walkways, and landscaping. One Community Global believes that open sourcing these materials will bring awareness to the many benefits of sustainable building and encourage others to want to make a positive global change that will benefit all inhabitants of the planet. As an open source material, these tutorials are designed to be easy to follow, replicable, cost-efficient, and ultra-sustainable. The resources that we freely offer can be implemented as individual elements or can be followed and integrated for the complete design of all components. We will continue to update this tutorial as we construct all of this and more as part of our 7-sustainable villages construction project.
WAYS TO CONTRIBUTE TO EVOLVING THIS SUSTAINABILITY COMPONENT WITH US
SUGGESTIONS ● CONSULTING ● MEMBERSHIP ● OTHER OPTIONS
CLICK THESE ICONS TO JOIN US THROUGH SOCIAL MEDIA
RESEARCHERS FOR THIS COMPONENT:
Alvaro Hernández: Open Source Tech Consultant, Developer
Carol Nguyen: Civil Engineer
Charles Gooley: Web Designer
Daniela Andrea Parada: Civil Engineering Student
David Na: Project Management Adviser/Engineer
Zhiheng “Samson” Su: Civil Engineer
Yomi Sanyaolu: Mechanical Engineering Graduate and Technical Writer
Yuran Qin: Web Designer
Julia Meaney: Web and Content Reviewer and Editor
SUSTAINABLE ROADWAYS, WALKWAYS, AND LANDSCAPING DETAILS
Sustainability plays an important role in improving the quality of life, protecting our ecosystem, and saving energy, water, money, and other resources for future generations. Details of sustainable roadways are divided into the following sections, with information on pavement types (flexible, rigid, composite, alternative options), roadway process overview, pavement recommendation, specific conditions to take into consideration, pavement structure layers, roadway drainage and collection, and fire department access requirements. Furthermore, in the “Walkways” section, the following topics are discussed in detail: street types, streetscape elements by street type, sidewalk widths and zones, constrained sidewalks, and intersection design. In addition, One Community’s landscaping will pass the Leadership in Energy and Environmental Design (LEED) certification for meeting the standards for sustainable design and maintenance, rainwater management, equipment used to clean the building exterior and hardscape, and protection of the environment.
We discuss all this and more with the following sections:
- Pavement Types
- Pavement Designs
- Process Overview
- Preparing a Pavement Recommendation
- Project Specific Conditions to Consider
- Roadways Drainage and Collection
- Fire Department Access
- Water Catchment
- Streetscape and Walkway Design
- Walkways
- Landscaping
- ADA Requirements
- Parking Lot Design Standards
- Handrail Design Standards
- Stairway Design
- Bicycle Design
- Road Design Specifics
- One Community’s Pavement and Walkways Plan (Case Study)
- Open Source Content Coming Later
- Resources
- Summary
- FAQ
- Glossary
PAVEMENT TYPES
Pavement is a structure that consists of layers of varying thickness, composition, and material, whose primary purpose is to accommodate design loads specific to a project. A properly designed pavement should his e exceptional ride quality, skid resistance, light reflectivity, and drainage. Pavements can generally be categorized into three types: flexible, rigid, or composite.
Flexible pavements, often referred to as asphalt pavements, combine multiple layers of aggregates and bitumen in the development of their structure. Aggregates are broad to coarse material that is typically made of sand, crushed stone, gravel, and recycled concrete, used for construction purposes. Bitumen is asphalt that is made from the distillation of petroleum and is black, viscous, and sticky in nature. Its application is generally used in road construction and repairs, roofing, and waterproofing. Rigid pavements, on the other hand, are typically constructed with a layer of cement concrete over a base layer. Lastly, composite pavements combine and utilize both asphalt and concrete properties, but are mostly used for maintenance and service instead of construction.
In the following sections, we go into detail expanding upon the different pavement types, their characteristics, makeup and material, and pros and cons. Concluding this section, we reveal why we have chosen specific pavement types for our design and where they will be implemented in our project.
FLEXIBLE PAVEMENTS
Flexible pavements are those in which the surface course consists of an asphalt-bound structural layer that is underlain with a non-rigid base such as an aggregate base. This type of pavement is engineered to bend or flex when loaded and distribute traffic loads to the underlying layers.
Below is a typical section view for flexible pavement:
The surface course is the topmost layer of flexible pavement that has direct contact with vehicular loads. The main function of the surface course is to provide a skid-resistance surface, friction, and drainage for the pavement. It should be watertight against surface water infiltration with a thickness of approximately 1 to 2 inches.
The Binder course is also constructed using aggregates and bitumen but with lower quality materials than those used for the surface course. The thickness is about 2 to 4 inches. The function of the binder course is to transfer the loads coming from the surface course to the base course.
The base course distributes the loads from the top layers to the underneath layers. It provides structural support for the pavement surface and is constructed with hard and durable aggregates which may either be stabilized or granular or both. The thickness of the base course is about 4 to 12 inches.
The subbase course is located beneath the base course and its functions are the same as the base course. If the subgrade soil is strong and stiff, then there is no need for the subbase layer. Granular aggregates are used to construct the subbase course. The thickness of the subbase is approximately 4 to 12 inches.
The subgrade is the bottommost layer, it is a natural soil layer that receives and absorbs the loads coming from above and is the foundation for the pavement system. The subgrade should be strong enough to withstand the stresses from the above layers, but it is also important to ensure the stresses from the upper layers are within the limit of the subgrade’s capacity.
For more information about flexible pavement layers, please visit the following website.
FLEXIBLE PAVEMENT CHARACTERISTICS
Flexible pavement’s ability to withstand applied loads without failing significantly depends on the strength of the subgrade. It maintains low flexural strength, which designates the ability to resist deformation before its breaking point. Unlike rigid pavements, flexible pavements do not require expansion joints due to their ability to expand or contract under different temperature conditions. Nevertheless, flexible pavements often require higher costs of repairs, ranging from $2-$3 per square foot, although repairments should not be needed for 10 to 20 years with proper maintenance.
TYPES OF FLEXIBLE PAVEMENT MATERIALS
Various types of hot mix asphalt materials can be used to design flexible pavement. The most common are: Dense Graded Hot Mix Asphalt (HMA), Rubberized Hot Mixed Asphalt Gap Graded (RHMA-G), and Open Graded Friction Course (OGFC). These materials and their details are described below:
Dense Graded (HMA): Dense Graded (HMA) is the most common mix that can be used as a surface course and it can be recycled to yield zero-waste materials. In order to achieve a steady and non-porous surface, the aggregate in the mix will be uniformly graded and laid. In addition, for the purpose of increasing its durability and resistance to endure extreme weather and temperature conditions, the aggregate can be treated and the asphalt binder can be modified. For aggregate, it can be a one-time seal treatment, but it will require reapplication every seven years for maintenance. Most asphalt pavements will require some sort of treatment every five to seven years to extend the pavement design life and longevity. Some common seal treatment products include Behr Premium Wet Look Sealer, Eagle Natural Seal, Glaze ‘N Seal, Foundation Armor, Seal Krete, Dominator Sealer, and Metropolitan Materials Aggreseal.
Rubberized Hot Mixed Asphalt Gap Graded (RHMA-G): Rubberized Hot Mix Asphalt Gap Graded (RHMA-G)’s composition consists of hot-mixed asphalt, recycled crumb rubber, aggregates, and sand. In the mixture, some intermediate-size aggregate particles are omitted from the gradation curve, creating the “gap”. RHMA-G can be used as a surface course or non-structural wearing course, with a maximum thickness of 0.2 ft. It is the only type of gap-graded HMA that meets Public Resources code requirements for a specific amount of crumb rubber modifier (CRM) usage. RHMA-G has various outstanding benefits, including the ability to provide elasticity to a structural overlay, prevent reflective cracking, and resist mechanical stress caused by drastic temperature fluctuations.
Open Graded Friction Course (OGFC): Open Graded Friction Course (OGFC), also known as Open Graded Asphalt Concrete (OGAC) is a non-structural wearing course placed primarily on asphalt pavement. There are three common types of non-structural OGFC, including Hot Mix Asphalt-Open-Graded (HMA-O), Rubberized Hot Mix Asphalt-Open-Graded (RHMA-O), and Rubberized Hot Mix Asphalt-Open-Graded-High Binder (RHMA-O-HB). This type of flexible pavement material can help to minimize vehicle water splash, manage excess runoff, improve pavement friction and skid resistance, and lessen headlight glare to reduce accidents during rainy days. Furthermore, as opposed to Dense Grade HMA, OGFC provides a permeable surface, which can significantly reduce the volume of runoff during wet seasons.
ASPHALT ROAD ADVANTAGES
There are many advantages to asphalt roads compared to rigid roads.
- Asphalt roads generally cost $2-$3 per square foot. This is significantly lower than the price of concrete roads, which range from $6-$8 for the same square footage.
- Asphalt road requires less installation time as a result of its ability to harden quickly once it’s laid. The road surface becomes driveable the same day it’s installed. Concrete road, on the other hand, requires a longer “curing” process to maximize its strength and this period can take up to 30 days depending on the type of traffic it experiences.
- Asphalt roads provide the benefits of an even and quiet driving surface, better skid resistance during wet conditions, and the flexibility to expand and contract during extreme temperature and pressure conditions.
- In contrast to concrete, asphalt roads generally require simpler maintenance and repairs.
- Lastly, asphalt is made of completely recyclable materials, which can be processed and reused.
ASPHALT ROAD DISADVANTAGES
Despite having various advantages, asphalt roads also include several drawbacks.
- Some of these determinants arise from the material processing for recycling. This process releases greenhouse gases, specifically carbon dioxide, which contributes to climate change.
- In addition, although asphalt road repairs are relatively simple, it requires more maintenance in comparison to rigid roads. With a lifespan of only ten years, asphalt is not considered a preferable option for long-term projects.
ASPHALT ROAD MAINTENANCE AND REHABILITATION
There are three types of maintenance: preventative, corrective, and emergency.
Preventative maintenance refers to improvements, such as surface treatments, that are applied to the pavement to slow the progression of distresses and failures and reduce the need for maintenance. Preventative maintenance is the most important type of maintenance because, if properly done, it significantly reduces the chances of corrective and emergency maintenance from being needed. Preventative maintenance consists of surface treatments that are typically required every 5-7 years due to gradual surface wear, pavement cracking, and weather/climate conditions. A handful of DIY surface treatments are given in the “Dense-Graded HMA” paragraph above. Other treatments performed by contractors can include fog and slurry seals.
Corrective maintenance is generally performed to repair minor to intermediate distresses such as pavement loss of friction, nonsevere longitudinal and transverse cracking, and bumps or sags. These types of distresses are usually inspected by an engineer in the field who performs a diagnosis on the distress. Depending on the severity of the distress, maintenance can be done to repair the roadway hazard.
Emergency maintenance is performed when there are severe distresses that risk the health and safety of the public or can significantly reduce the design life of the pavement. These distresses generally include potholes, alligator cracking, raveling, and deep depressions.
RIGID PAVEMENTS
Rigid pavements are those with a stiff surface course that is typically a slab of Portland cement concrete (PCC) over underlying layers of stabilized or unstabilized base or subbase material. These types of pavements rely on the substantially higher stiffness of the concrete slab to distribute the traffic loads over the wider area of underlying layers and subgrade.
The surface course of rigid pavement is a concrete slab that is in direct contact with vehicular loads. When added some texture, it can offer friction to the vehicles to provide skid resistance. The thickness of the concrete layer is about six to twelve inches.
The layer underneath the surface course is the base course. This layer is constructed with crushed aggregates. Its function is to support the concrete slab by taking additional loads. It can also provide a subsurface drainage system and a stable platform to construct rigid pavement. The base course thickness should be in the range of four to twelve inches.
The subbase course will not be necessary if the traffic loading is light, i.e. when the loading does not exceed 100,000 pounds or approximately 46,000 kilograms. This layer is in contact with the subgrade soil. It consists of lower quality aggregates than the base course. Its main functions are to provide support for the top layers and to prevent the intrusion of fines from subgrade to top layers. Fines are defined as any particles, such as rock, that are finer than ¾ of an inch. The subbase layer also helps to improve drainage, and its thickness varies from four to twelve inches.
The existing, bottommost layer is the subgrade. This layer is compacted to provide a stable platform for concrete pavement. The subgrade soils are subjected to lower stresses than the top layers since the stresses will reduce with depth. The pavement layers above the subgrade should be capable of reducing stresses imposed on the subgrade soil to prevent the displacement of subgrade soil layers.
Click here for more information about different layers of rigid pavement.
RIGID PAVEMENT CHARACTERISTICS
A common characteristic of rigid pavement is its durability and long life span. Rigid pavements generally have a lifespan that lasts 30-40 years compared to that of flexible pavement which averages 10-15 years. It has high bending strength, which is defined as the resistance to applied loads before failure. As mentioned in the previous section, rigid pavements cost more than asphalt pavements, with a unit cost of approximately $6-8 per square foot. However, since rigid pavements require less maintenance on a regular basis, it would yield lower maintenance and repairs cost. The structural integrity of rigid pavements is less dependent on the strength of the subgrade, therefore, the soil quality of the subgrade can be lower. Unlike flexible pavements, concrete pavements do not possess the capacity to expand and contract under extreme temperature conditions, so expansion joints are required. The average strength of fully cured, common concrete ranges from 3,000 to 6,000 psi, and the time period required to gain strength in this range depends on each type of concrete. More on this will be discussed in the proceeding sections.
TYPES OF RIGID PAVEMENT MATERIALS – CONCRETE
The most common rigid pavement materials include Portland Cement Concrete (PCC), Rapid Strength Concrete (RSC), and Roller Compacted Concrete (RCC).
Portland Cement Concrete (PCC): This is the most common type of concrete used. Its main ingredients consist of Portland cement, water, fine aggregate (crushed stone or gravel), coarse aggregate (natural sand or finely crushed rock), supplementary cementitious materials (to improve durability, workability, and strength), and chemical admixtures (to modify or enhance certain properties of fresh or hardened concrete and ensure its quality during different processes). Portland cement can develop a compressive strength of over 3,300 psi in approximately one week. It’s used for the installation and construction of new pavement, street widening, sidewalk/parkway, reconstruction, and rehabilitation. PCC is also designed to resist environmentally induced degradation for more than 100 years.
Rapid Strength Concrete (RSC): RSC has the capacity to develop strength in a short time period. Specifically, in approximately two hours, it can gain a strength of over 3,000 psi. With this characteristic, RSC is generally used for rapid construction and projects with tight scheduling requirements. RSC also includes accelerated strength gain admixtures, which help increase concrete workability and durability. RSC is typically used for Jointed Plain Concrete Pavement (JPCP) replacement, rehabilitation, preservation of aging infrastructure, and tight scheduling reconstruction.
Roller Compacted Concrete (RCC): RCC’s ingredients include several basic elements of concrete, such as water, cement/fly ash, sand, and fine and coarse aggregates such as crushed stone or gravel. In contrast to PCC, RCC is produced with a lower water-to-cement ratio, yielding zero slump. Because this concrete has lower water content it must be compacted with a vibratory roller though, to increase its strength. RCC often requires no form, steel reinforcement, hand finishing, or joint saw-rutting. It also requires less maintenance since RCC doesn’t need surface sealing or overlays. Thus, it often results in lower material cost, post colling, and formwork. At a normal pace, RCC usually takes roughly seven days to gain a compressive strength of 2,500 psi. The maximum compressive strength it can gain ranges from 4,000 to 10,000 psi, so RCC will not deform easily under large amounts of concentrated loads. Like PCC, RCC is designed to resist environmentally induced degradation for more than 100 years.
CONCRETE ROAD ADVANTAGES
Despite the fact that concrete roads are often more expensive than asphalt roads, they still have several significant benefits. First, rigid pavements have a longer design life, which is more than 30 years. They also require less maintenance on a regular basis compared to flexible pavements. In addition, similar to asphalt, concrete can also be processed and recycled in the future. With great compressive strength that can withstand large pressure and loads, concrete roads are ideal for high truck volume. Furthermore, concrete is more resistant to the freeze-thaw cycle, which is the process of water seeping into cracks along the surface and expanding as it freezes. Lastly, concrete also results in producing less pollution and harm to the environment compared to asphalt.
CONCRETE ROAD DISADVANTAGES
Besides the advantages mentioned in the previous section, concrete roads have two main drawbacks. First, while they do not require frequent maintenance and repairs, when maintenance is needed, it is more difficult and expensive to fix. Concrete has very low tensile strength, so it can easily crack under extreme conditions. In some severe cases, replacement may be needed for the entire slab. In wet conditions, due to concrete’s smooth surface properties, it can also cause slipping accidents. Texture can be added to the road surface to resolve this problem but at the cost of increased noise pollution and reduced ride quality. In addition, concrete roads require a longer installation time, with a minimum waiting period of seven days, compared to flexible roads which can be used 24 hours after installation.
COMPOSITE PAVEMENTS
Composite pavements consist of both flexible and rigid layers over underlying stabilized or unstabilized base or subbase materials. The existing rigid pavements will be overlaid with flexible pavements layers, such as HMA, OGFC, or RHMA. Composite pavements are the combination of asphalt and concrete pavements, therefore, they can compensate for each other’s weaknesses and mitigate different functional problems such as subgrade rutting, fatigue cracking, concrete erosion, and PCC loss of friction.
Figure: Typical Cross-sections of Composite Pavements
COMPOSITE PAVEMENT ADVANTAGES
As composite pavements consist of both flexible and rigid layers, they possess the main advantages of both types. Composite pavements have adequate skid resistance thanks to the HMA surface course while also offering a smooth surface for driving comfort. The hot mix asphalt layer is laid on top of the rigid layer, so it will be strongly supported by a stable foundation and protected from the intrusion of de-icing salts and surface water.
COMPOSITE PAVEMENT DISADVANTAGES
Composite pavements’ main disadvantages include reflective cracking issues and their high costs compared to traditional asphalt pavements. Reflective cracking is roadway distress that only occurs on asphalt pavements that have been laid over a concrete pavement. The distress is not load-related but is caused by the movement of the PCC layer underneath the asphalt surface. Reflective cracking typically occurs where the expansion joints are located and can result in several pavement problems such as premature failure of the surface asphalt as well as water infiltration which can lead to problems with the base underlying the pavement.
Pavement Options Comparison Table – Click to open the open source spreadsheet in a new tab
ALTERNATIVE PAVEMENT OPTIONS
Besides the most common types of pavement listed above, there are other alternatives to consider as well. For instance:
- Porous asphalt pavement helps with water infiltration to minimize excess runoff.
- Decomposed granite can be used for various applications such as driveways, patios, and walkways.
- Paving stones have great durability, low maintenance, and are easily repaired.
- Permeable interlocking concrete pavers (PICP) allow the open graded subbase to absorb excess stormwater.
- Brick pavement is cost-efficient and can be used for driveways and courtyards.
- Gravel pavement is affordable and does not demand challenging installation.
- Turf blocks can be designed for construction with low traffic volume.
The following section provides detailed information about the specific applications for each pavement option, their advantages, disadvantages, and their unit price for the engineer to make comparisons and select the optimal solution for each project.
POROUS ASPHALT
Porous pavement is different from types of pavement in that it allows water to infiltrate instead of simply running off. This allows for the collection of rainwater or the slowing of runoff. It is generally used in parking lots, but it can also be used as a road pavement option. Porous asphalt costs from $1-$3 per square foot. The porous area has 16 inches of stone in the subgrade and 5 inches of the surface mix and construction costs run from $10 to $12 per square foot with installation.
The overall cost of permeable pavement is usually more expensive than regular pavement because of the planning it takes. Laying permeable pavers is a multi-step, time-consuming process that requires a professional, otherwise, the environmental (or aesthetic) benefits will not be attained.
DECOMPOSED GRANITE
Decomposed granite is a derivative of granite that occurs when granite begins to flake or crumble away. It has many applications, such as patios, driveways, walkways, roads, etc. It can be used for many diverse purposes, however, due to a higher price, it is not recommended for large road or parking lot paving projects. The cost of decomposed granite ranges from $1-$3 per square foot.
PAVING STONES
Paving stones are just as they sound: natural stones, bricks, or concrete that are used primarily for walkways, driveways, and even sidewalks. They have many benefits such as durability, easy repairs, low maintenance, and aesthetic customizations. This option is also easier to install and can be a DIY project. Paving stones are priced from $2.5-$3.7 per square foot.
PERMEABLE INTERLOCKING CONCRETE PAVER (PICP)
PICP is another option for major walkways. Permeable Interlocking Concrete Paver (PICP) is the most common type of permeable paver. In PICP design, the paver is not permeable itself, but the joints are designed to allow water to infiltrate. These permeable pavers consist of solid paving units that are connected using permeable joints. The joints are filled with permeable aggregates that allow for water to flow into the open-graded subbase below. PICP is estimated at about $10.95 per square foot which includes the paver, underdrain, and subgrade material.
BRICK
Brick pavers are made of clay cast in form and bricks (of various shapes) that are arranged in essentially any pattern of one’s choosing. This form of paver is generally used for driveways and courtyards. At a price of $5.00 per square foot, it is an affordable and easy to install option.
GRAVEL
Gravel pavement is a common pavement option for those that are trying to conserve money and seek an easy installation. This option is more catered for the design of a driveway, temporary parking lot, or short roadway. The one downside with going with gravel pavement is that it needs consistent maintenance. Gravel can be purchased at a price of $1.00 per square foot, which is by far the cheapest option.
TURF BLOCK
Turf block is a concrete grid where grass is seeded into the open grid spots. This option is typically seen in the construction of a driveway or parking lot with low traffic volume. However, it is not recommended because it is not ADA compliant. Turf block generally costs $4-$6 per square foot.
Alternative Pavement Options Comparison Table – Click to open the open source spreadsheet in a new tab
For the construction of our road and walkways within the property, in the Earthbag Village, and around the Duplicable City Center, One Community decided to go with what we think will be the most sustainable options: porous pavement and decomposed granite. Sustainability is a core value and major design factor for our projects. After much research, we believe that porous pavement and decomposed granite are not only more sustainable alternatives to the conventional asphalt or concrete roads and walkways, but are also more cost-efficient, lower maintenance, and in the case of decomposed granite, more aesthetically pleasing. In the following sections, we go into detail and compare the different pavements. In the following sections, we go into detail to compare the different pavements and discuss why we have decided to move forward with certain pavement types for each respective area.
PAVEMENT DESIGNS
Pavement designs are an important consideration that must be decided upon within the early stages of a development project. What material you plan to use, your budget, and who or what the road will be servicing are all important topics that must be covered before moving forward with the installation of a roadway. In the following sections, we discuss the different types of materials that are available, share their cross-sectional views with standard material depth, and provide a cost analysis table that can be used to estimate your approximate project costs.
For each type of pavement, there are some characteristics that need to be taken into consideration. In general, when designing a pavement engineers will obtain information about its components, layers, construction process, maintenance, repairs, advantages, and drawbacks in order to select the optimal design for the project. In the following section, porous asphalt, porous concrete, decomposed granite, and rigid pavements are discussed. In the porous pavement section, its components, layer functions, construction procedures, maintenance, advantages, disadvantages, potential stormwater runoff demands, and general and structural design to withstand the traffic loading are listed. The porous concrete section includes the pavement’s structural design, applications, construction and maintenance considerations, advantages, and disadvantages. For decomposed granite, information about materials required to construct a decomposed granite pathway, placement and installation guide, maintenance, and repairs will be discussed. Lastly, the concrete pavement section will describe different types of concrete, procedures for new, widening, and reconstruction projects, and pavement preservation materials needed for rigid pavement construction and rehabilitation.
We discuss pavement designs in detail with the following sections:
- Understanding Pavement Structure Layers
- Porous Asphalt Design
- What are Porous Pavements?
- General Porous Asphalt Design, Construction, and Maintenance
- Porous vs. Conventional Pavements
- Components of a Porous Pavement
- Porous Asphalt with Stone Reservoirs
- Advantages and Disadvantages of Porous Asphalt (With Stone Reservoirs)
- Structural Design
- Site Guidelines and Considerations
- Potential Stormwater Runoff Demands
- Structural Design to Ensure the Porous Pavement Withstands the Anticipated Traffic Loading
- Construction Procedures for Porous Pavement
- Maintenance for Porous Asphalt
- Porous Concrete Design
- Decomposed Granite Paving Design
- Flexible Pavement Design
- Rigid Pavement Design
- Rigid Pavement Types
- Types of Concrete
- Pavement Joints
- Transition Panels, Terminal Joints and End Anchors
- Continuously Reinforced Concrete Pavement Terminal Joint Types
- Jointed Plain Concrete Pavement
- Joint Seals
- Dowels and Tie Bars
- Base Interlayer
- Texturing
- Pavement Smoothness
- Procedures for New, Widening, and Reconstruction Projects
- Engineering Procedures for Pavement Preservation
- Rigid Pavement Rehabilitation
UNDERSTANDING PAVEMENT STRUCTURE LAYERS
Pavement design involves the determination of the type and thickness of pavement surface course, base, and subbase layers. The main factors that go into determining these details include traffic load, service life, budget, and climate. Pavement structures are composed of one or more layers of selected materials placed above the subgrade. The following are the basic pavement layers for a roadway:
SUBGRADE
The subgrade is a layer of in-situ native soil (or improved/treated soil) and is the bottom layer or “formation level” of roadways and pavement, upon which pavement structural layers sit upon. The subgrade can either be compacted or remain uncompacted depending on the type of pavement installed and the load type that the pavement will experience. For example, loose uncompacted subgrade serves well for porous pavements that are designed for lighter traffic conditions. The uncompacted subgrade also allows porous pavements to have better infiltration due to increased void spaces in the soil. On the other hand, well-compacted subgrades are ideal for heavier traffic conditions, which increases the strength and load-bearing capacity of road pavements.
SUBBASE
This consists of treated or unbound aggregate or granular materials which can be situated above the subgrade. Subbase works as a foundation or platform for the base.
BASE
The base is composed of selected, processed, and treated aggregate material which is then placed immediately above the subbase.
SURFACE COURSE
Represented through one or more pavement layers, the surface course is engineered to provide skid resistance, minimize climate effects, distribute and accommodate traffic loads, enhance surface drainage, minimize surface water infiltration, reduce noise from tire/pavement interaction, and more.
NON-STRUCTURAL WEARING COURSE
To increase the longevity of pavement life and protect it from tire/pavement interaction and various environmental factors, a non-structural course is placed on top.
OTHERS
The inclusion of additional layers depends on either the pavement type, subgrade, or existing soil conditions. These layers may include:
- Interlayers
- Bond Breakers
- Tack Coats
- Prime Coats
- Leveling Courses
- Working Platform
For additional details of subgrade, subbase, base, surface course, non-structural wearing course, and other layers of pavement, please refer to the Highway Design Manual from Caltrans, Topic 602 – Pavement Structure Layers, Index 602.1 – Description.
Fig. 602.1 – Basic Pavement Layers Of The Roadway
POROUS ASPHALT DESIGN
WHAT ARE POROUS PAVEMENTS?
Porous pavements are permeable surfaces that allow for sufficient infiltration of precipitation and control the flow and volume of stormwater runoff. They are also excellent “green” pavement alternatives because they reduce the amount of pollution that would otherwise be sent into stormwater drainage systems and discharged into local water systems. Porous pavements are separated into two types: porous asphalt/concrete and permeable pavers. Porous asphalt and/or concrete pavements are poured and laid in a similar fashion to their impervious counterparts, but the finer materials such as sands are removed to create a higher void ratio in the mix. Due to a large amount of void space, water is able to flow through the surface and into the pavement base layer which is filled with aggregates that are typically 2” in diameter, allowing for stormwater storage and recharge. Permeable pavers, or permeable interlocking concrete pavement (PICP), are solid concrete paving units with joints that have openings to allow for water infiltration. These joints are filled with large stone aggregates that help water to move freely and into the ground. Depending on the design these systems can help recharge the groundwater table and/or collect and treat the water before it is released into the drainage system.
Porous asphalt often consists of a top surface (porous asphalt), a choker course, a base/subbase course, an optional layer which is filter fabric, and a subgrade layer.
The surface course thickness is about 2 to 4 inches. It is a standard hot-mix asphalt with reduced amounts of sand or fines, this leaves stable air pockets in the asphalt, making it permeable. The main function of this layer is to provide a stable wearing surface and allow the infiltration of water to the stone recharge bed.
The stabilizing or “choker” course is underneath the surface layer. It consists of a clean single-size crushed stone that is smaller than the stone in the recharge bed, this helps stabilize the surface for paving equipment. Its thickness is about 1 to 2 inches.
The next layer is the base/subbase. This layer is relatively thicker than the others, with thickness ranging from 18 to 36 inches. This layer is an open-graded base consisting of crushed stone or crushed gravel with no greater than 5% passing the No. 200 sieve (0.0029″ (75µm) nominal sieve opening with a typical wire diameter of 0.05mm).
The final and deepest layer is the subgrade, which is a layer of the existing soil. Its primary function is to allow infiltration of stormwater.
For more information on porous asphalt pavements, click here.
GENERAL POROUS ASPHALT DESIGN, CONSTRUCTION, AND MAINTENANCE
The benefits of utilizing porous asphalt include the reduction of stormwater volume, improvement of runoff quality, and significantly lower carbon emissions from the manufacturing of this material in comparison to other pavement types. These pavements are a sustainable way to build a flat lot where little to no puddles will form.
Porous pavements are commonly used as light-duty roadways or parking facilities. Their designs allow them to act as water retention and infiltration systems. When determining the design of porous pavements for a project it is essential to consider three aspects. First, determine the soil type that supports the pavement. Infiltration will take longer to occur in low-permeable soils such as silty clays, therefore building a failsafe is recommended. Second, for the maximization of infiltration, soil beds should have flat designs. Finally, the designed pavement should be able to withstand the pressure of paving equipment with no distortions. For this reason, single-size aggregates greater than 3 inches need to be avoided.
For the construction of porous pavements, the subgrade should be excavated with the use of a soft footprint. Porous pavements also need to be built to last in order to ensure protection from heavy equipment. Additionally, a fabric filter is necessary to preserve the porous pavement until sufficient vegetation is established. Proper maintenance increases the lifespan of the pavement, this includes refraining from the use of abrasives such as sand for the snow/ice control and avoiding materials that can clog the pavement. Lastly, providing the pavement with a regular sweeping or blowing of debris will keep it from clogging and therefore ensure a longer life span.
POROUS VS. CONVENTIONAL PAVEMENTS
The porous asphalt surface uses minimal compaction to allow infiltration of water. It is fairly permeable because it possesses air voids that range from 15 to 20% of the total asphalt volume. Porous asphalt is classified as open-graded asphalt concrete. Additionally, for the base layers of porous asphalt, a geotextile fabric is utilized as a separation layer to ensure that the fine material from the subgrade does not migrate to the recharge bed. The void ratio for the base layer tends to range around 40%. Lastly, the subgrade of porous asphalt is compacted lightly to ensure infiltration.
On the other hand, conventional flexible pavements prevent the infiltration of water because they are dense-graded concrete. With air voids lower than 8%, these pavements are categorized as relatively impermeable. Their features include reduced stress for the below layers and decent ride quality. The base layer of a conventional flexible pavement is also densely graded (close to 100% compaction) for the reduction of stress to the subgrade. Similarly, in order to provide a durable platform, the subgrade for this pavement is compacted to its maximum density.
COMPONENTS OF A POROUS PAVEMENT
- High permeable asphalt surface
- Stone recharge bed/reservoir
- Stabilizing layer
- Geotextile fabric
- Uncompacted subgrade
POROUS ASPHALT WITH STONE RESERVOIRS
Porous asphalt pavements with stone reservoirs are considered to be low-impact development technology that further strengthens sustainable and environmental efforts. A stone reservoir is a highly permeable layer of crushed stone that stores treated runoff temporarily as the water infiltrates the uncompacted subgrade. This layer also works as a structural layer and requires voids of at least 40%. As the water filters, contaminants such as pollutants are removed. Initially, the water drains through the porous asphalt, it is then held in the stone reservoir to later drain into the underlying layers and eventually restore groundwater. The stone reservoir’s thickness is commonly influenced by the infiltration rate of the soils and the quantity of water needed to be controlled. Overall, stone reservoirs provide essential stormwater management in a cost-efficient manner.
ADVANTAGES AND DISADVANTAGES OF POROUS ASPHALT (WITH STONE RESERVOIRS)
ADVANTAGES:
Porous asphalt mitigates the effects of heat islands by reducing the temperature of stormwater, a process that especially occurs in the summer. In colder temperatures, the ice and snow that rest on the pavement tend to melt at a faster rate. Porous asphalt improves visibility and hydroplaning during wet weather while absorbing tire/engine noises. Another benefit of using porous asphalt with stone reservoirs is the reduction of contaminated runoff water and the refilling of groundwater reservoirs due to increased permeation and less surface evaporation. This asphalt also increases and improves the water allocation to nearby plant roots and reduces stormwater runoff volume. Due to these advantages and various others, porous asphalt has been recognized by LEED and other rating systems for green construction.
DISADVANTAGES:
Although porous asphalt provides various advantageous sustainable practices, it also causes some limitations. Maintenance is crucial for this pavement because dirt and debris can easily clog the surface, vacuuming and sweeping would be two viable options to reduce this occurrence. Due to its permeable qualities, porous pavements should not be placed in areas where toxic spills can occur. Additional design considerations are necessary when designing sloped porous pavements, commonly seen in terraced parking and underground berms. For this, there are higher initial pavement costs, but the long-term benefits of utilizing the pavement outweigh this con. In addition, since porous asphalt allows water to infiltrate through the pavement surface and then into the ground, after a period of time the soil has the potential to become fully saturated. When this situation happens, the infiltration process may not be as effective causing the excess water to rise to the surface of the pavement resulting in flooding. In order to prevent this problem, porous asphalt pavement typically has a perforated pipe under the pavement that collects and transfers stormwater runoff to a designated discharge location. Side gutters can also be added as emergency backup drainage. During wet seasons when it rains frequently, if the drainage system under the road surface gets clogged and does not operate sufficiently, gutters can be used as an alternative to prevent stormwater overflow.
STRUCTURAL DESIGN
- Stone recharge bed typical thickness: 12 to 36 inches
- Composed of crushed stones/aggregates with 40% voids
- Hydrologic characteristics:
- Subgrade infiltration rate: 0.1 to 10 inches/hour
- Time to drain, stone recharge bed: 12 to 72 hours
- Choker coarse thickness: Minimum 1 to 2 inches
- A layer of single-sized stones that stabilizes the surface in order for paving equipment to be used
- These stones are smaller than those in the stone recharge bed
- Non-woven geotextile
- Prevents fine materials from migrating to the stone reservoir
- Uncompacted subgrade
SITE GUIDELINES AND CONSIDERATIONS
The depth to the bedrock to address seasonal high groundwater levels should be a minimum of two feet or greater. The soil supporting the porous asphalt should have an infiltration rate ranging from 0.1 to 10 inches/hour. Additionally, a recommendation provided by the University of New Hampshire suggests that the bottom of the stone reservoirs be placed at 60% of the local frost depth. However, this can be altered depending on the region of the project. In order to ensure the retention of water, it is advised to keep a flat bottom for the infiltration bed along with the inclusion of berms located underneath the pavement surface. The slope of parking areas must range less than 5% and any slope greater than this should be terraced with berms in between. For impervious areas, their runoff should be routed to infiltration beds. The ratio from impervious to pervious areas should be less than 5:1 and a 3:1 ratio may be used for areas susceptible to sinkholes.
POTENTIAL STORMWATER RUNOFF DEMANDS
- The hydrologic design of porous pavements should be performed by a licensed engineer.
- The potential overflow should be included in the design to prevent stored stormwater from reaching the surface layers. This will involve perforated pipes in the stone reservoir that are connected to the discharge pipe.
- The left diagram in the image below demonstrates a stone edge design for overflow and the right diagram illustrates a drop inlet design.
Stone edge design (left) and drop inlet design (right)
STRUCTURAL DESIGN TO ENSURE THE POROUS PAVEMENT WITHSTANDS THE ANTICIPATED TRAFFIC LOADING
- Porous pavements can last for more than 20 years.
- The structural requirements are not significant for porous pavements carrying light traffic only.
- For porous pavements expected to carry heavy truckloads, the structural design should follow standard AASHTO 93 design procedures.
Recommended minimum compacted porous asphalt thicknesses
CONSTRUCTION PROCEDURES FOR POROUS PAVEMENT
The use of oversized tires and/or tracks is suggested for the excavation of the subgrade soil to provide minimal soil compaction. After the final grade has been excavated, lay out a fabric filter overlapping a minimum of 16 inches. Any excess fabric that is greater than or equal to 4 feet should be folded over the stone bed. As mentioned previously, Porous pavements do tend to have lower weight-bearing capacities due to their air voids. Porous pavement is suggested to be the final step for roadway construction so that any heavy equipment does not damage the roadway and to prevent any construction spills from seeping through the pervious pavement. The installation of drainage piping is recommended wherever necessary and the recharge bed should be placed with care to avoid fabric damage. The thickness of these layers ranges from 8 to 12 inches and they are later compacted with a light roller. Utilizing a stabilizer course ensures that the aggregate is properly sized and interlocked with the recharge bed aggregate; a layer thickness of one inch is then placed. Once completed, 1-4 inches of porous asphalt is placed and then compacted with a 10-ton static roller which passes over 2 to 4 times. Lastly, traffic is restricted for a minimum of 24 hours after the final roll.
MAINTENANCE FOR POROUS ASPHALT
The upkeep of porous asphalt is necessary to increase pavement life and provide quality roads in accordance with design standards. Various maintenance methods will be further described below.
Porous asphalt should be inspected annually, particularly during and after rain events. Inspectors must observe and check for any standing surface water, doing so guarantees effective surface infiltration rates. Power-washing is suggested 2 to 4 times within a year, this can also be substituted with vacuum sweeping. Regularly scheduled sweeping removes organic debris that may have accumulated such as leaves and trash and the adjacent areas will receive erosion and sedimentation control. Additionally, repairs can be made with nonporous asphalt, but these repairs must not occur on more than 15% of the total area because water would not be able to filter through as efficiently.
During colder seasons, utilize deicing chemicals that melt the snow. This process lowers water’s freezing point and when proper snow maintenance is achieved, meltwater will readily drain. With proper meltwater drainage, the formation of black ice can be avoided thus making preventative measures unnecessary. However, prior to storms, the application of treatments for anti-icing are suggested for traffic safety. When maintained improperly, premature clogging will occur and the snow will stockpile on the porous pavements. Precipitation combined with compacted snow causes further complications but can easily be corrected with additional deicing. Therefore, instead of corrective cleaning, the most effective approach is preventative cleaning.
POROUS CONCRETE DESIGN
WHAT IS POROUS CONCRETE?
Porous concrete, also known as pervious concrete, is a pavement that effectively captures runoff water. Its properties primarily depend on the water-to-cement ratio, the compaction level, and aggregate quality. In comparison to traditional concrete, porous concrete does not contain fine aggregates. Little to no sand is added which allows for larger voids, because of this water filters through ensuring sufficient drainage rates. Voids typically range from 15 to 25% meaning that up to 80% of a year’s runoff water can infiltrate the pavement. During this process, studies indicate porous concrete can remove up to 65% of undissolved nutrients from runoff and up to 95% of sediment in runoff. Porous concrete is commonly used in driveways, residential streets, and parking lots because they are roads with low traffic volume. Although the cost of this pavement ranges around 15% higher than traditional concrete, it provides necessary stormwater management. The service life of porous concrete is approximately 20 years. Overall, permeable concrete is deemed an effective instrument to manage stormwater runoff, so much so that it receives LEED credits.
ADVANTAGES AND DISADVANTAGES OF POROUS CONCRETE
ADVANTAGES:
Porous concrete reduces contamination found in waterways and stormwater runoff which then recharges the groundwater. By doing so, the size and number of storm sewers can be reduced along with the use of fewer retention ponds. Permeable concrete has the ability to capture the “first flush” also known as the runoff containing the highest number of contaminants. Flooding is alleviated through the reduction of peak stormwater water volume and velocity and standing water, such as puddles, appears less frequently thus reducing slip hazards. Puddles also create algae in minor cracks which can lead to larger cracks, especially when the water freezes. By reducing puddles, the lifespan of the pavement is extended. It has also been found that permeable concrete is cooler in temperature in comparison to other pavement types. With the reduction of heat, fewer heat islands will develop in the cities that utilize porous concrete. Lastly porous concrete has overall reduced costs.
DISADVANTAGES:
Although porous concrete provides various beneficial qualities and aspects to project developments, it also possesses limitations. Porous concrete requires an extended period of time for curing. Construction practices are specialized for this pavement. It is also sensitive to the amount of water incorporated into the mix. Due to its properties, standardized concrete tests are difficult to perform, therefore reducing the knowledge engineers can obtain for quality control and assurance. Discovered so far is the knowledge that permeable concrete must be utilized in areas with limited heavy vehicle traffic. Soil types should be analyzed before the placement of all pavements, but special designs for porous concrete are required when working with expansive or frost-susceptible soils. Sites with high groundwater levels require that more attention be paid to design requirements. This is due to the higher chance for such sites to have potentially damaging groundwater seepage from below.
STRUCTURAL DESIGN
The structural design of porous concrete consists of a minimum of three layers including the pervious concrete, the base, and the subgrade. Reference the image below for an illustration of the design.
- Porous Concrete:
- Thickness of 4 to 8 inches
- The materials used to create porous concrete include Portland cement, water, and open-graded coarse aggregate
- Crushed Aggregate:
- Suggested by some, but not demonstrated in the illustration below is a 1 to 2 inch layer
- Commonly composed of crushed aggregate that measures half an inch
- Base/Subbase Layers:
- Thickness measuring 6 to 12 inches
- Three-inch aggregate may be used for this layer
- Filter Fabric:
- Optional usage for water filtration
- Subgrade
Hydraulic designs are determined after structural requirements have been met. Adjustments should be made if the thickness of the porous concrete is insufficient.
APPLICATION
Porous concrete can be used for hardscaping such as parking walkways, pathways, pool decks, residential roads, and driveways. This pavement may also be used for the floors of zoos, aquatic centers, and greenhouses. Various other uses include seawalls and stabilization of slopes. These technical qualities of porous concrete are used for evaluating its applications: the flexural strength ranges from 150 psi to 550 pounds per square inch and the compressive strength ranges from 500 to 4000 pounds per square inch. Yet, the shrinkage rates for permeable concrete are less than those of standard concrete.
CONSTRUCTION AND DESIGN CONSIDERATIONS
CONSTRUCTION CONSIDERATIONS:
The placing of porous/permeable concrete requires tools to execute processes such as strike-offs, jointing, and compaction during its construction phase. For instance, straightedges are instruments used to strike off excess concrete from the surface to smooth it. This is also known as floating or screeding. A straightedge may have a round edge made for floating and a square edge made for cutting. This tool helps ensure that the proper grade is applied. When finishing the permeable concrete, a steel roller must be used to consolidate the pavements. At this time the final height of the project/concrete should also be set. Next, jointing is completed in order to prevent the development of unexpected cracks.
Note: Permeable concrete can have relatively low water content and still remain porous. However, due to the lack of moisture, the placement of the concrete must be completed in a timely manner. The completion of this process results in inspection through The American Concrete Institute Code.
DESIGN CONSIDERATIONS:
Generally, the drainage design of permeable concrete should incorporate the removal of excess stormwater and drainage overflow. For the prevention of water contamination, install the concrete no less than 4 feet above the groundwater table’s seasonal high. The permeability of the porous concrete must be 8 inches per hour and the bedding layer must drain within 72 hours after a rain event. Throughout the lifespan of the porous concrete ensure that the pavement is not overworked, particularly with vehicle traffic. To also increase the concrete’s lifespan, keep from using sand or salt to defrost any ice. Refrain from placing the pavement in areas with high levels of contaminants and toxins such as gas stations. Areas with high wind erosion that contributes to blown sediment are not recommended either. Pavement slopes should on average have a 2% grade/slope and should not be greater than 5%. Lastly, a second method must be provided to ensure that the water can still enter the stone reservoir.
MAINTENANCE FOR POROUS CONCRETE
Periodic maintenance is required for the removal of surface debris such as sand and dirt that collect within the voids. Power vacuuming and pressure washing are methods that will restore the pavement’s porosity. Providing this maintenance also allows for the system to remain long-lasting and effective. Additional maintenance includes refraining from oil changes over porous concrete. In cold weather conditions, porous concrete can withstand the freeze-thaw cycles, yet snow piles must not melt over the pavement for the system can clog with sediments. The removal of ice and snow with the use of snowblowers is recommended, but deicing chemicals should not be used.
DECOMPOSED GRANITE PAVING DESIGN
WHAT IS DECOMPOSED GRANITE?
Decomposed granite is a material composed of fine granite particles which originate from naturally weathered and eroded solid granite. It is commonly used in landscaping to establish transitions between formal gardens and the natural environment. Decomposed granite is also used in xeriscaping due to the material’s permeability and capacity to break down. For instance, when decomposed granite migrates, its ability to break down reduces the chances of accumulating in the surrounding environment which would cause a negative impact on the surrounding areas. Contrarily, gravel regularly causes issues because pieces of the gravel will travel onto the lawn or plant beds and remain there. Therefore, decomposed granite’s ability to break down is advantageous.
Furthermore, there are three notable types of decomposed granite: loose, stabilized, and decomposed granite with resin. The least expensive of the three is loose decomposed granite. Although this pavement type becomes muddy during rainy and wet conditions, it is best suited for low-traffic areas and garden beds. On the other hand, stabilized decomposed granite is less susceptible to erosion because a stabilizer is mixed with this material. As a result, this type of pavement maintains a longer lifespan with low levels of maintenance. Lastly, decomposed granite with resin is the strongest and most costly of all three pavement types. The material is not as permeable in comparison to loose and stabilized decomposed granite but works well in driveways and high traffic areas. Decomposed granite with resin reflects similar characteristics to asphalt and is the most durable.
ADVANTAGES AND DISADVANTAGES OF DECOMPOSED GRANITE
ADVANTAGES:
From aesthetics to sustainability, decomposed granite provides various benefits to the user. Notably, this pavement has a reasonable price range and is easy to install. The amount of maintenance the pavement requires is low, making it a desirable solution for xeriscaping. Additionally, loose and stabilized decomposed granite has high permeability, indicating there would be little to no runoff water. The variety of colors provided is also beneficial to a project because, in order to increase albedo (surface light reflection) and reduce heat buildup, lighter colors can be used. Loose decomposed granite is a reliable option as mulching material and all three types of decomposed granite provide a natural appearance.
DISADVANTAGES:
On the other hand, decomposed granite has various detriments that should be discussed prior to installation. For instance, when refills are necessary, the same pavement color may be challenging to find. It is recommended that a portion of the original material be stored on hand to avoid this issue. Decomposed granite with resin will cause higher levels of water runoff because it is not as permeable. This consideration is essential because the site layout needs to drain water properly. Lastly, as mentioned previously, loose decomposed granite becomes muddy with the addition of water which can later be tracked indoors and ruin flooring as well as cause sediment transport.
MATERIALS NEEDED TO CONSTRUCT A DECOMPOSED GRANITE PATHWAY
Below, we list the materials required to construct a Decomposed Granite (DG) pathway.
- Decomposed Granite:
- Utilize decomposed granite with stabilizer pre-mixed or soil stabilizer can be purchased.
- The most popular decomposed granites are Desert Gold and Southwest Brown.
- Header Boards: Wooden boards that are used to create a barrier between the paved area and adjacent surface. It can also serve as formwork for the paved area.
- These average 4 inches in width.
- It is recommended to use pressure treated redwood and plastic extruded materials that are not only waterproof but also will last/hold over time. Plastic is an unsustainable option that we’d prefer not to support, but we plan to explore as part of our plastic recycling strategy repurposed plastic for creating materials like this. If we can’t use repurposed plastic, we will use pressure-treated wood (unless we can find something more sustainable).
- Weed Barrier:
- This material is optional but retains water for plants.
- Compactor Option:
- Heavy roller.
- Vibrating plate compactor.
- Manual Hand Tamper.
- Rake.
- Hose with a nozzle that can create a “shower” flow pattern or similar.
- Measuring Tape, Calculator, Paper, Pencil.
DECOMPOSED GRANITE PATHWAY INSTALLATION
The first step is to design and indicate the pathway location. Once achieved, the detailed design will help aid with estimating the amount of decomposed granite needed for the project. Begin by installing header boards first then add the optional weed barrier. Then add the first layer of decomposed granite, ensuring that it is level. Finally, add the remaining layers of decomposed granite and include any last finishing touches, including maintenance.
PREPARATION
The subgrade, also known as the material placed underneath the decomposed granite, is highly recommended to be an aggregate base. Pathways require approximately 4 inches of aggregate base and driveways require approximately 6 inches. This material needs to be thoroughly dampened and compacted to at least 92% to 95%. Each compaction is dependent on the application.
PLACEMENT AND INSTALLATION GUIDE
- The DG should be placed over a compacted aggregate base or subgrade. If greater than 3 inches install in 2 inches lifts.
- 3-4 inches for walkways or pathways.
- 5-6 inches for driveways or roadways.
- When placing material, be sure the material depth is even throughout.
- Thoroughly dampen the DG.
- Water and compact each layer if installed in 2 inches lifts.
- Check DG to ensure the water has penetrated the full depth of the material.
- Wait 6 to 24 hours until the material is firm enough for compaction by 1 to 3-ton roller.
- When completed, walk the finished surface for any high or low areas and fill as needed.
- Allow 3 to 4 days for DG to completely dry.
MAINTENANCE AND REPAIRS
Over time loose aggregate can begin to appear and accumulate. The most manageable solution is to water the surface, in doing so the excessive surface material will re-compact. Large repairs require new decomposed granite with Pro-Bond. This is completed by following the section regarding Placement and Installation. Smaller repairs are achieved by compacting the area with hand tampers.
FLEXIBLE PAVEMENT DESIGN
The design of a flexible pavement must first begin with a preliminary analysis of the soil on the site prior to initiating any designs. By doing so, soil characteristics can be identified, which will allow for design engineers to create a pavement that reflects the needs of the soil. Additionally, the anticipated loads placed on pavement structures helps determine what design aspects will work best with each roadway type. Three variables that greatly affect design are soil strength, traffic volume and expected axle loads. Once design engineers obtain this information, they progress to the next step which concerns substantial pavement design. One main design interest for flexible pavements is the layer thickness and composition; both of which can be derived by using the California Bearing Ratio Design Procedure or AASHTO’s Design Equation for Flexible Pavements. As the first approach focuses on the physical properties of soil using field tests, the latter is based on an equation utilizing wheel load and pavement serviceability.
Due to various judgment calls, the final chosen design should be detailed in a design analysis by the pavement engineer so that these decisions can be reviewed and approved. Maintenance and rehabilitation efforts must then be scheduled in order to upkeep the pavement in satisfactory conditions. A further analysis of these processes is provided below.
PRELIMINARY ANALYSIS
Investigations must be conducted to determine soil characteristics and vehicle load expectations. A preliminary data collection is initiated by the Pavement Design Engineer. To obtain this information, the engineer can review the Pavement Condition Survey (PCS), the Roadway Characteristics Inventory (RCI), the Straight Line Diagrams (SLD), as well as previous plans. Additionally, it is highly recommended to conduct a field review to ensure that all design objectives will be met. All documentation collected within the last year regarding rehabilitation procedures and pavement conditions should be obtained and analyzed. To ensure that pavement engineers design the most reliable flexible pavement design, it is essential to test and investigate various factors of the site such as surface infiltration, rainfall, topography, groundwater, moisture conditions and soil uniformity. Roadways will undergo different processes depending on if the project site has had prior pavement types or if the new pavement will be placed on a previously unpaved road.
For a project site that has prior pavement types, the Pavement Design Engineer will use all of this information to evaluate the probable causes of distress of the existing pavement (given there is one) along with providing methods as to how to prevent these distresses from reoccurring. If lower layers have caused issues for instance that have caused rutting previously, the designer should identify solutions such as reconstruction. The District Materials Office should also be contacted to evaluate the project.
The preliminary analysis of previously unpaved roads includes obtaining data from various soil analysis procedures. Engineers should collect studies for the field dry density, particle size, and specific gravity. For instance, a sieve analysis using a field sample would determine the distribution of grain size and provide further insight as to what type of soil resides on site. The specific gravity will exhibit the amount of voids the soil contains. In addition, shear tests and consolidation tests must be carried out to determine the stress and settlement characteristics. If the soil type is primarily composed of clays, linear shrinkage is important to test for.
For both paved and unpaved roads, subsurface explorations should be incorporated in projects as their results may reveal areas where subgrade conditions are of poor quality. For instance, analysis of moisture content indicates where the soil has softer layers. If the moisture content is not taken into account in the design process, the strength of the pavement and its lifespan will be reduced. Testing various soil conditions also allows engineers to predict the performance of the pavement. A geotechnical process called soil boring should be used to provide soil profiles and to identify data such as moisture content and density. Soil borings use a drilling method to create a vertical hole in the soil. The depth of this penetration indicates the depth of frost penetration, but this must not be less than 6 feet under the grade. Through this process, engineers collect samples of the soil that allow them to perform an analysis that provides a better understanding of the layer properties. This further helps engineers to design pavements in a way that will prevent settlement, reduce cracking, and increase pavement design life. Provided below is an image of four soil borings.
Image of Four Soil Borings
Further preliminary analysis includes predicting vehicle type and traffic volumes in order to classify the roads and design pavements that will be able to withstand anticipated traffic. One design aspect that must largely be considered for this is the magnitude of the axle load. Axle loads refer to the weight applied through all wheels connected to a given axle, and can also be interpreted as the load that is transferred to the axle of a vehicle. Although the gross weight of pneumatic-tired vehicles play a role in considering design elements, the axle load of expected vehicles is more significant to pavement design. Axle loads influence the design more heavily as the wheel loads of one axle have little interaction with wheel loads of another, which occurs due to large spacings between axles. On the other hand, vehicle loadings are more relevant than load repetition when it comes to pavement design because a small increase in gross weight is equivalent to a large increase in traffic volume. For instance, increasing gross weight by 10% would be proportionate to increasing traffic volume by 300%. Due to these considerations, pneumatic-tired vehicles are categorized in three major groups. Group 1 consists of passenger cars and pickup trucks, Group 2 consists of two-axle trucks, and Group 3 consists of three to five-axle vehicles. Yet, because various forms of traffic are composed of various forms of pneumatic-tired vehicles, a further classification has been devised that considers both traffic and vehicle type. These categories are as follows:
- Category I: Traffic composed of primarily Group 1 vehicles such as passenger cars and pickup trucks. Group 2 vehicles, two-axle trucks, take up no more than 1% of the traffic.
- Category II: Traffic composed of primarily Group 1 vehicles, but containing up to 10% of Group 2 vehicles.
- Category III: Traffic composed of up to 15% trucks, but no more than 1% of vehicles are from Group 3.
- Category IV: Traffic composed of up to 25% trucks, but no more than 10% of vehicles are from Group 3.
- Category V: Traffic composed of more than 25% of trucks.
These various aspects help provide an appropriate design index for pavement plans. The design index uses traffic categories for loads and volumes along with a roadway’s level of service in order to assign a numerical value from one to ten. The increase in the assigned numerical value indicates that there will be increased design requirements for the pavement. The table below illustrates the Pavement Design Index.
For more information regarding a roadway’s level of service, refer to the section concerning Road Design Specifics.
Table 2: Pavement Design Index
Additionally, more information regarding pavement design life, traffic considerations, soil characteristics, and life cycle cost analysis are further explained in the section concerning Project Specific Conditions to consider.
CALIFORNIA BEARING RATIO DESIGN PROCEDURE
One procedure that is frequently used in flexible pavement design is the California Bearing Ratio (CBR) design procedure. The purpose of this analysis is to provide a strength test that measures the stress the soil can resist, relative to the amount of stress a standard soil is able to resist. In this case, a material’s bearing capacity is compared to the bearing capacity of well-graded crushed stone. The well-graded crushed stone is composed of high quality material and possesses a CBR of 100%. To calculate the CBR of a soil use
The ratio demonstrates resistance to penetration, therefore testing the soil’s shear strength.
For a laboratory CBR test, a soil sample is prepared in a steel mold. Prior to the CBR test, the soil being used must pass through a 20mm sized sieve. Sieves sort soil by their size and assist engineers to classify the soil more efficiently, while also removing large pieces of gravel. Water content of the soil should also be considered prior to performing the CBR test. Most commonly, the moisture content of the soil will either be the optimum water content or the field moisture. Once the moisture content is determined, five kilograms of the soil taken from the site are prepared through a series of intricate steps. Then, the soil is placed in a cylindrical mold and is compressed with a steel plunger measuring 50mm in diameter. The load it takes for the steel plunger to compress the soil is recorded when the penetration reaches a depth of 2.5mm and a depth of 5mm. Using the loads obtained from the tests, the CBR is calculated. The values obtained for penetrations vs load are also plotted on graphs. This video demonstrates the process explained above for the in lab California Bearing Ratio Test. Equipment can be seen in the first image below.
The CBR test can also be completed on site (in-situ) using similar equipment, shown in the image below on the right. Since saturation of the soil cannot be controlled on the field, the laboratory test is more accurate and the more preferable approach. Using a vehicle to stabilize the equipment, a cylindrical plunger penetrates the soil at a uniform rate of 1mm per minute. The loadings are then obtained at each quarter millimeter and used to calculate the CBR values. This video demonstrates an in-situ CBR test. Although the procedures vary from lab to in situ, both provide similar processes and determine the strength of the soil.
California Bearing Ratio Test Apparatus
California Bearing Test Apparatus In the Field
These requirements and procedures ensure that the pavement layers’ thickness is able to properly distribute traffic induced stress so that underlying layers will not deform. Additionally, the compaction of pavement layers is commonly carried out and plays a large role in roadway construction. With the CBR of the soil being obtained, it is then up to engineers to provide a design that ensures that traffic will not add intolerable amounts of compaction to the pavement. Engineers recommend using a soaked CBR for projects sites that have no prior information regarding pavement performance. This is illustrated in the image below and undergoes a similar procedure to the dry test. On the other hand, for sites that maintain existing pavement, in-situ tests can be used because the subgrade material possesses the maximum expected water content.
California Bearing Radio Testing
The use of CBR design procedures are prominent in three primary layers: subgrade, subbase course and base course. These designs are dependent on select materials and also rely on soil properties. Each layer requires specific conditions to be met in order for the design to be executed properly. These are described for all three layers below.
SUBGRADE:
For subgrades using flexible pavement, the natural density must be able to resist the densification that occurs under traffic. In some cases, the subgrade may be compacted in order for its natural density to resist the densification. The table below indicates the depth of the pavement dependent on the percentage of compaction that is needed to prevent densification. When these required measurements are not met, the subgrade must be removed or compacted. In the table below, “PI” refers to the plastic index of soils, while “LL” refers to the liquid limit of soils. In order to calculate the plastic index, the plastic limit and liquid limit must be determined. The liquid limit and plastic limit are two out of the three measurements that make up the Atterberg Limits. The plastic limit of the soil is a percentage that is calculated using the dry weight of the soil when it becomes brittle, and will therefore show the lowest water content of the soil. This can be found by remolding fine-grained soil with the palm of your hand to make it into a cylinder shape. Once the soil can no longer form a cylinder of 3.2mm diameter or less without cracking, it has reached its plastic limit. The dry weight of this soil will then be recorded and used to find the plastic limit percentage. The liquid limit is a percentage that indicates at what point the water content of a soil changes the soil’s behavior from a plastic state to a liquid state. Once these are both established, the plastic index is calculated by subtracting the plastic limit from the liquid limit. This difference, known as the plastic index, shows the soil’s range of water content for which the soil will remain plastic. Using the design index chart above, each roadway type is assigned a subgrade depth based on given percent compaction.
Table 4: Depth of Compaction for Select Materials and Subgrades (CBR20)
SUBBASE:
Subbase courses that are designed with flexible pavement are typically chosen to be made with materials that are readily available. As shown in the table below regarding Maximum Permissible Design Values for Subbases and select materials, subbases that have a design CBR above 20 are categorized as the designated subbases, while those with CBR values under 20 are categorized as the selected materials. When designing flexible pavement, a distinction is made between select materials and designated subbases. Designated subbases consist of soils that are blended or processed; this includes cinders, disintegrated granite, and caliche. As an economical alternative, materials that have been stabilized with commercial additives such as portland cement are commonly used. On the other hand, select materials will be coarse grained soils and are generally uniform or processed soils. Materials such as disintegrated granite, limerock and coral are categorized as select materials and should be considered when determining which available pavements most fit the budget of the project. For materials such as these , grading requirements, which determine aggregate size distribution, must be considered. In order to meet these standards, an aggregate size of 3 inches is highly suggested.
A subgrade may only be assigned a design CBR value higher than 20 if the gradation and plasticity requirements for subbases are met. In some cases, a subbase may not be needed where the design CBR value for the subgrade ranges between 20 to 50. Select materials for subbases and their compaction requirements coincide with the subgrade requirements shown in the table above. A design requirement for subbases is that under no circumstances can cohesionless fill have a compaction lower than 95% and under no circumstance can a cohesive fill have a compaction lower than 90%. Table 6 provides further subbase requirements based on CBR design. For design purposes, laboratory tests for CBR on subbases must be either equal to or higher than the assigned value provided on the chart. This is because gravelly materials that are commonly used for subbases have shown that the CBR values obtained in the field are lower than those obtained in the laboratories. By ensuring that the design CBR is larger than the assigned value, it guarantees a reliable design. The figure below shows additional requirements for suggested limits.
Table 6: Maximum Permissible Design Values for Subbases and Select Materials
BASE COURSE:
The flexible pavements used for base courses must be composed of high quality materials that are able to resist high stresses occurring near the surface of the pavement. There are maximum densities that are generally required for the base courses used in flexible pavement design which should not fall below 100%. In order for the materials to develop their necessary strengths, they must follow the guide specifications that correlate with each material type. As many guide specifications can be found through research based on each specific material type, AASHTO provides Guide Specifications for Highway Construction and specifies further details.
Due to the discrepancies between processing samples from the site and obtaining the laboratory CBR tests, materials that are purchased for the application of the new pavement design are assigned CBR values by the supplier. Design CBRs for common base materials do not vary by much. For instance, graded crushed aggregate, water-bound macadam, and hot mix must have a design CBR of 100, while limerock and stabilized aggregate have a design CBR of 80. Base courses must also be designed with a minimum thickness of 4 inches. Any roads classified with a level of service A through D must not have a compacted thickness of less than 6 inches.
Table 8: Minimum Thickness of Pavement and Base Course
REQUIRED STRUCTURAL NUMBER DESIGN PROCEDURE: AASHTO’s MODEL
A different procedure that can be used instead of CBR is the American Association of State Highway Officials (AASHTO) equation/model. This design equation calculates the Required Structural Number which gives a value that indicates the pavement thickness that must be attained in order to support the vehicle loads. AASHTO’s flexible pavement design equation can be utilized in various ways, but it will most commonly be used to find the Structural Number. The image below illustrates AASHTO’s Design Equation. Also provided below are the descriptions of each variable. These calculations are provided by this guide that further details information concerning multiple variables, provides design examples, and elaborates on deeper concepts. Design tables are shown and explained throughout the guide and must also be followed in order to ensure a practical pavement design.
AASHTO Design Equation For Flexible Pavement
AASHTO Design Equation Input For Flexible Pavement
The inputs for AASHTO’s design equation for flexible pavement are explained in the following:
W18, as presented in the equation above, is the accumulated Equivalent Single Axle Load over the duration of the project, also known as the 18-kip ESAL. The Flexible Pavement Design Manual provides a summarized explanation of the process to obtain the 18-kip Equivalent Single Axle Loads, yet, this manual suggests referring to the Project Traffic Forecasting Handbook Procedure Topic No. 525-030-120 for a more intricate description. EALF is dependent on various factors such as structural capacity, type of pavement, and thickness and can be obtained in the AASHTO Guide for Design of Pavement Structures, 1993 Appendix D. On the other hand, the resilient modulus, , is the elastic modulus under repeated loads for recoverable strain. Resilient modulus can be found by dividing the axial/applied stress (σd) by the axial strain (εr), MR = σd/εr. Another way to interpret resilient modulus is a measurement that calculates the roadbed soil’s stiffness. The constants in this equation include Standard Deviation and Change In Serviceability. A Standard Deviation of 0.45 is commonly used for these design calculations in order to ensure that variability for predictions in traffic loads are accounted for. The Change in Serviceability demonstrates the difference between the serviceability of a new roadway and the serviceability of a roadway that requires rehabilitation or reconstruction. As these values are most commonly assumed to be 4.2 for serviceability of a new roadway and 2.5 for serviceability of a road in need of rehabilitation, a value of 1.7 is most frequently used for the Change In Serviceability.
Additionally, AASHTO’s design equation for flexible pavement incorporates a factor of safety. Engineers must include a factor of safety in all calculations in order to ensure that there is a margin of safety in their designs that will adhere to requirements detailed in code. The incorporation of a safety factor ensures a stable and long lasting design. For this equation, the safety factor is applied through the Reliability Value (%R) on which the Standard Normal Deviate (Zg) is dependent. Each reliability value is assigned a standard normal deviation. Shown in the first table below are the recommendations of reliability for roadways. Each value is based on the classification of urban and rural roads, in addition to the classified function of the roadway. The second table below demonstrates the Standard Normal Deviate that corresponds to the reliability percentage. Since the Standard Normal Deviate is an assigned value taken from a table, it can also be acquired from various resources such as those researched online, in addition to this guide.
Table 3.1: Suggested Level of Reliabilities for Various Functional Classifications (AASHTO, 1993)
Table 3.2: Standard Normal Deviates For Various Levels of Reliability (AASHTO, 1993)
Furthermore, for the incorporation of various layers, an additional equation provided by AASHTO is used. The layered design analysis provides a structural number for each layer that is dependent on layer coefficients and drainage coefficients. Once again depending on the information provided, the equation can be used in various ways. For example converting the structural number to use it to calculate layer thickness. Typical layer coefficients are 0.44 for hot mix asphalt, 0.2 for road mix and 0.13 for aggregate base. Agencies will ensure that layer coefficients are set for materials in design policies. For the drainage coefficient, the design engineer must decide what level of drainage the pavement is planned to achieve. Once identified, engineers will use a table provided by AASHTO’s 1993 design guide to determine which coefficient to use. It is commonly recommended to use the drainage coefficients with higher values in order to design improved drainage conditions. For roadways that have existing drainage issues, it is highly recommended to design a drainage system prior to the new pavement. All in all, there is no simple solution for this equation as various combinations can be calculated for layer thickness. Due to multiple calculated combinations, practical requirements for thickness in addition to economic analysis must be taken into consideration by design engineers. This layered design analysis formula and an image that demonstrates the layered thickness is provided below.
Figure That Demonstrates the Layered Thickness
QUALITY ASSURANCE AND QUALITY CONTROL
Construction details must be thoroughly described in the plans and provided to the District Construction Office in order for further specifications to be determined. These details include constructability issues, construction time, traffic control plans for the duration of the construction time, base type, and more.
To ensure quality assurance for a project, standards, guidelines, policies, trainings, and other systems need to be established. These efforts provide assurance that components of the project’s design or structure will integrate essential requirements and that overall, engineers will produce and execute quality designs. To further guarantee compliance with all standards and guidelines, quality control reviews must be done. Additionally, a new Pavements Design Summary Sheet must be prepared when major changes have been made to the project. These summaries must include data that document the reasoning behind any changes and must be relayed to the State Pavement Design Engineer. It must always be documented clearly whenever aspects of the project do not adhere to policies. The greatest liability that exists within pavement design is friction course selection. It is suggested that the Pavement Design Engineer familiarize themselves well with the Departments Friction Course Policy which the Flexible Pavement Design Manual details. This manual illustrates the requirements for designs of dense graded friction courses and open graded friction courses. As there are various conditions to standards and policies, engineers must keep note of their reasoning for all design aspects of their project to ensure that other individuals are able to understand and contribute to the process.
FLEXIBLE PAVEMENT WIDENING
In order to conduct pavement widening, the Pavement Design Engineer must identify the existing pavement structure and what it consists of. Various considerations need to be taken into account based on the characteristics of both the new and existing pavements. Since pavement widening may incorporate lane additions or trench widening, the new pavement will be designed to match the existing pavement and the overlay pavement. Ensuring that the surface elevation of the new pavement matches that of the existing one is essential. A minimum requirement for pavement widening is using materials for the new pavement that are compatible with materials of the existing one, in addition to implementing drainage under the existing pavement. Underdrains must be extended from the existing pavement and directed to an outlet located beyond the new pavement. If these conditions are not able to be met, then Headquarters Pavement Reviewers should be consulted with proposals for alternatives.
When planning for pavement widening, it is suggested to schedule preservation procedures within the same time frame. Arranging the pavement widening and preservation procedures collectively ensures a uniform appearance and that traffic flows are not disrupted for an extended period of time, therefore making the project cost and time effective. Further, a thorough evaluation of the adjacent pavement structure should also be carried out. It is deemed to be inefficient and undesirable to widen a roadway without planning to correct existing structural distresses or ride quality issues. A non-structural wearing course may need to be applied over both the widened and existing pavement. This is expected to bring both pavement types to the same life expectancy. In combining the rehabilitation with the widening, long-term costs and traffic delays will be minimized.
Just as a preliminary analysis must be completed for the pavement design, roadway evaluations must be done prior to pavement widening. Survey data must be provided so that current pavement conditions can be analyzed and properly replicated. This includes reviewing past maintenance history and following the Site Investigation Guide to perform an official site investigation. The data reviewed may be taken from Ground Penetrating Radar data that provides information such as layer thickness and as-built material properties. As some projects may cover side drains or other drainage systems, the new road design must accommodate for water catchment.
Water Catchment Road Design
Longitudinal joints are created when a new hot mix asphalt lane is paved adjacent to an existing lane. The edge of the existing lane is defined as a cold joint because the surface has already hardened and creates a discontinuity with the new batch of hot mix asphalt. If the lanes are composed of different pavement types, deterioration of the pavement will occur more rapidly. It has been shown that joints in the wheel path have larger rates of deterioration and so it is important that longitudinal joints are placed where the proposed lane lines will be located, as shown in the image below. This will reduce excessive loadings being placed onto the joint. Therefore, reducing joint deterioration suggests that the joint/lane line be shifted so that it lays further in the existing pavement. The following four steps must be taken in order to properly construct a longitudinal joint:
- Compact the existing/first paved lane’s unsupported edge
- Overlap the second lane’s mix with the first lane
- Properly rake the mix off the first lane
- Compact the longitudinal joint with a steel wheel roller
Challenges may arise when constructing longitudinal joints. For further instruction regarding techniques that help resolve these issues, refer to Design Considerations for Flexible Pavement Widening. Engineers should also consider designing the longitudinal joint with a geosynthetic interlayer which is placed prior to the application of a full-width overlay. By using the geosynthetic interlaye, reflective cracking at the joint is reduced.
Geosynthetic Interlayer Which is Placed Prior to the Application of a Full-width Overlay
An additional design requirement for widening flexible pavement is that the base material of the widened section must be designed with a strength that exceeds or matches the current base strength. Therefore, selected pavement mix designs must be taken into consideration when widening roadways. The objective of a mix design is to ensure that the properties of the materials are optimized and that common distresses of the material are mitigated. The percentage of additives in the pavement mix is intended to optimize the pavement’s performance and cost effectiveness. For instance, the appropriate stabilizer must be chosen for subgrades or bases; but more commonly for bases. A stabilizer is an additive poured prior to the asphalt in order to strengthen the area. There are three stabilization methods: mechanical, chemical, and bituminous. The most common stabilization for pavement widening is based on a chemical hardening process that occurs between the additive and the soil. Chemical additives specifically used for widening projects such as lime, cement, and fly ash are carefully selected based on sieve analysis and the Atterberg Limits. The stabilizer chosen is also dependent on factors like soil characteristics, design life and environmental conditions. For the addition of lanes and shoulders, it is highly suggested that stabilization be incorporated, but this is not recommended for trench widening strips.
In instances where the new flexible design pavement is thicker than the existing pavement, a minimum of 0.15 feet of overlay is added to the surface. In occasions where the pavement adjacent to the widening exhibits vast amounts of cracking, it is recommended to conduct in-place recycling instead of following through with the widening project. In-place recycling methods use machinery that reuses the current pavement to rehabilitate it by breaking down the pavement and remixing it. Most widening projects add 2 to 4 feet of pavement to the existing roadway. This narrow addition calls for specific equipment in order to adequately compact the added pavement. Most commonly, the widened pavement is the area where the outermost wheels of trucks will travel. Since these sections will be worn down the most, variations in quality will be exposed. Districts have therefore adopted a system for “matching cross-sections” of pavements, ensuring that the intersection of the plane reflects what is needed. This system takes into consideration previous instances where different bases were used or where moisture became trapped beneath the original pavement. Be sure to review approaches that certain districts have devised based on site location in order to minimize errors with different methods of in-place recycling.
MAINTENANCE / PRESERVATION
Various maintenance techniques are used for flexible pavements in order to extend the longevity of the pavement life. Multiple considerations should be taken into account based on the pavement condition. We have provided information on these techniques below.
OVERLAY:
An overlay is a layer of pavement that is added to an existing pavement surface to help prolong the life of a road. When cracked pavement is not able to be removed due to insufficient material, crack relief layers may be used as an overlay. The minimum thickness of the overlay is dependent on the vehicle loading types. Thin overlay treatments that are used for corrective or even preventive purposes must measure less than 1.5 inches. Caltrans uses these thin treatments with an ensured layer thickness of 1.2 inches. This overlay will not only insulate the pavement that has been cracked, but it will also help with the reduction of stress concentrations. Overlays should not be placed over pavements that are not structurally sound.
Caltrans utilizes three main maintenance overlay types: Dense Graded, Gab Graded, and Open Graded. For project sites, one of the three overlays is chosen. The application of an overlay is a process commonly used in combination with other treatments like, for example, a Stress Absorbing Membrane Interlayer (SAMI) that Caltrans often applies. The below image shows these three types of overlays and descriptions follow beneath.
Three Main Maintenance Overlay Types For Project Sites
I. Dense Graded: Helps mitigate raveling, minor cracking, and skid problems and adds waterproofing. Dense graded mixes contain aggregate that ranges in size and has low air voids. As this is a dense graded thin overlay, it is commonly used to overlay Portland cement concrete or asphalt. These overlays have an average lifespan of 4 to 6 years, and at most 10 years. However, environmental conditions and the current pavement conditions directly affect the expected life.
II. Gap Graded: Helps mitigate flushing surfaces, reflection cracking, oxidation, skid problems, and raveling. The gaps within this overlay are produced by the reduction of fine aggregate content in order to accommodate the binding element, which in many cases is an asphalt rubber binder. Between these gaps, larger particulate rubber can be found and binder content ranges between 7 to 9% of the total overlay composition.
III. Open Graded: Helps mitigate noise problems, oxidation, minor surface irregularities, and skid problems. In open graded asphalt concrete, the amount of air voids will range from 15% to 25% of the overall composition, making the material highly permeable. Relative to other Hot Mix Asphalts, there will be a reduction in splash and spray, skid resistance, and wet pavement glare, in addition to the improvement of quick water drainage. Open graded friction courses should not be used in areas that frequently receive snow. Under proper conditions, the lifespan of an open graded overlay will be 4 to 6 years. General maintenance such as high-pressure cleaning is highly recommended in order to uphold life expectancy.
STRESS ABSORBING MEMBRANE INTERLAYER (SAMI):
A Stress Absorbing Membrane Interlayer, also known as a SAMI, is used prior to Hot Mix Asphalt or Micro Surfacing. It uses a binding agent that provides a waterproofing membrane that is flexible. SAMI is made up of a crushed aggregate that is combined with polymerized asphalt emulsion (the binder). The crushed aggregate may consist of limestone, local aggregate, or natural gravel. Aggregate size should be no smaller than 10mm and should be applied at a lighter spread rate than the binder. The installation of the SAMI is similar to that of a chip seal, discussed in the section below. When placing SAMI layers, it is recommended to obtain a consult from the District Bituminous Engineer, who is an individual that specializes in a distinct pavement material type.
Stress Absorbing Membrane Interlayer (SAMI)
A SAMI may also be used as a moisture barrier in cases where rippling is caused on the asphalt surface by moisture from the subgrade entering the pavement. Further, SAMI can be used to control cracking or reduce reflective cracking while extending the service life of a pavement. This method is able to reduce cracking with horizontally or vertically dissipated energy based on the design of the interlayer. Site weather conditions must be taken into consideration when applying a SAMI as in colder weather, loose adhesion between the aggregate and binder are more likely to occur and will create aggregate loss. Additionally, the polymerized asphalt emulsion should only be applied to dry surfaces when temperatures are well above 55º F and wind is not excessive.
PAVEMENT SEALS:
I. Chip Seals: These are suggested to be applied to roadways of lower speeds and volumes. However, in instances where proper application procedures are adhered to, chip seals may be used under other roadway circumstances. Chip seals are primarily used as a wearing course, an interlayer between new asphalt and the underlying pavement, in addition to being applied as part of the process for cape seals. Cape seals utilize a chip seal as the first layer and will then add a slurry seal (described below). The purpose of a chip seal is to provide a high-performance, skid-resistant surface and to seal cracks while protecting the aging pavement and underlying structures. Chip seals may also be used as interlayers in order to slow reflective cracking that begins to develop from the bottom of pavement structures. The application of chip seals is a three-step process. After a road has been swept, a uniform layer of an asphaltic binder is applied in order to seal the pavement surface. A chip spreader machine will then lay small stones immediately on top which will be set in place by rubber-tired rollers that compress the chips into the binder. The roadways are then given a final sweep to remove any loose rock. If a cyclical application of chip seals is planned for a site, it should be treated once every seven to ten years.
Road Sweeper
Chip Sealer
II. Slurry Seals: These may be used as a layer over for chip seals and can also be used for older pavements. They are most commonly applied onto residential streets every five to seven years. The purpose of slurry seals is to smooth the ride quality, restore flexibility that has been lost, and seal cracks. Yet, the distress of the pavement cracks must range between low to moderate, in addition to having a narrow crack width. Other reasons engineers utilize slurry seals include preventing water intrusion, revitalizing the rich black surface color, and protecting underlying pavement from sun damage. In some various instances, slurry seals can be used as a wearing course or a preparatory treatment prior to other maintenance. Furthermore, the components of a slurry seal mixture are well-graded fine aggregate, water, mineral filler, and emulsified asphalt. A thin layer is applied to a pavement surface using a slurry truck with a spreader box attached to the rear. As shown in the image below, workers will use squeegees to help spread the mixture and ensure areas are properly covered. After the slurry seals have been placed, you must wait 4 to 6 hours before opening the road to traffic.
Slurry Seal Applicator
III. Crack Seals: These are another type of pavement seal that is applied for a broader range of cracks. These include transverse cracking, centerline cracking, longitudinal cracks, and random cracking. This seal may not be used for alligator cracking as this form of cracking indicates structural deficiencies with the pavement itself. Crack seals are used to fill individual cracks in order to keep water intrusion from occurring. Two common crack fillers are sand slurry and rubberized asphalt. Once applied, successful crack seals will be finalized by being cleaned of their loose material with compressed air.
Crack Seals
IV. Fog Seals/Coats: These may also be applied as a pavement seal. These are composed of asphalt that is diluted and slow-setting. This asphalt is a specially formulated emulsion also known as thin liquid oil. The light application of this asphalt is most suitable for low-volume roads such as those that can be closed to traffic for up to 5 hours – the amount of time it takes for this coat to dry. The effectiveness of fog seals is limited to anti-oxidation roles which slow oxidative stresses and hardening in addition to anti-raveling roles which protect against the disintegration of the surface. This includes preventing water intrusions and rejuvenating older pavements. These seals not only help preserve underlying pavement, but also restore flexibility that has been lost through wear. Additionally, this method can seal narrow cracks and provide a deep black pavement color that is most often desired for roadway pavements. Fog seals are often seen as a light application that plays a similar role as seal coats. Extra precautions must be taken in order to avoid creating slick surfaces that induce skidding. These seals are more commonly used in desert regions in order to protect the new asphalt against oxidation. Typically, fog seals are applied on a cyclical basis every three to five years.
Fog Seal / Coat
MICROSURFACING:
Similar to slurry seals, microsurfacing is applied for the protection of underlying pavement and for the development of an improved driving surface. Roads that have been chosen as good candidates for microsurfacing must have narrow crack widths and low to moderate distress. They are most commonly done on streets that have large amounts of shade because as slurry seals rely on the evaporation of water, microsurfacing hardens without relying on heat or evaporation. It will then take up to two hours for the new surface to harden and for the road to be opened to traffic. The components that make up this mixture are small aggregates, water, asphalt emulsion, and some chemical additives. It is due to these chemical additives that microsurfacing hardens quicker than other seals. As shown in the image below, a continuous machine may be used for roadway segments that do not have sharp curves. These machines are able to carry large amounts of aggregate, water, and other additives due to their various compartments. In order to produce a smooth surface texture, a piece of burlap is dragged along the pavement while the microsurfacing is being applied. This treatment is completed every five to seven years.
Microsurfacing
POTHOLE PATCHING:
Pothole patching is a commonly known maintenance method for utility trenches and minor potholes. The development of underlying structural issues, however, would call for full-depth repairs. An effective technique that is commonly used for pothole patching cuts the pavement so that all loose material can be removed. The area must then be treated with quality hot mix asphalt and compacted with a small drum roller.
Pothole or Distress Patching
REHABILITATION
In order to accurately provide a reliant rehabilitation design, the condition of the pavement must be extensively investigated. This includes reading into performance history and analyzing the current structure of the pavement, in addition to performing various laboratory tests. Pavement surveys that should be considered during the field investigation focus on deflection and drainage. Tests such as a dynamic cone penetrometer (DCP) and a ground penetrating radar are two non-destructive surveys that aid the analysis of pavements.
When creating a strategy for rehabilitation, aspects such as future prevention and cost-effectiveness must be taken into account. The methods chosen must adhere to existing constraints and must address all existing pavement issues. Although these rehabilitation treatments restore the texture of the pavement surface and weatherproof the material, the structural capacity of the pavement and the ride quality are not increased. As mentioned for maintenance and preservation, multiple considerations should be taken into account when deciding which technique to utilize based on how the pavement presents itself.
HOT IN-PLACE RECYCLING (HIR or HIPR):
A technique of rehabilitation for addressing distressed surfaces and texture issues is Hot In-place Recycling (HIR). There are four main procedures to HIR:
- To begin, the surface is heated to induce the softening of the existing pavement.
- Then, scarification occurs, which removes the pavement.
- Afterwards, the material is recycled and remixed thoroughly with an aggregate or asphalt binder.
- The last step is paving and compacting the surface.
In addition there are three methods of HIR:
- Heater Scarification/Surface Recycling Method: The pavement is heated and re-worked in order to rejuvenate the top inch of asphalt. After scarifying the pavement, a rejuvenating agent is added to the mixture in order to improve the viscosity of the asphalt binder. Once the whole process is complete, the pavement is compacted. By using this recycling method, engineers can restore the surface to its preferable grade and cross section.
- Remixing Method: The top 1 to 2 inches of the pavement are heated, reworked, and rejuvenated. Aggregate is mixed into the new recycled material and is used as either a surface course or a binder. By adding the new aggregate the strength of the pavement will be improved. This remixing method aids in restoration of the pavement if the repaving method is not sufficient enough to provide the desired pavement properties. Yet, this process may only be carried out if the pavement has no more than one seal coat.
- Repaving Method: As done in surface recycling, the top inch of the pavement is heated, reworked and rejuvenated. But for the repaving method, an overlay is applied while the surface still holds a temperature of 200℉. At the end of this process, both layers are compacted. Repaving primarily eliminates cracking, raveling, and rutting in addition to focusing on deficiencies that occur within the top 50mm of the pavement surface. When engineers do not achieve the desired surface requirements using the recycling method, they undertake this process.
Scarification / Surface Recycling Method
Repaving Method
Hot In-place Recycling may be completed in a single-pass or multiple-pass operation. The typical depth of an HIR process reaches between ¾-inch to 2 inches of the pavement surface level. If there are shortcomings in the recycled asphalt pavement, then a new hot mix may be added. When additional stability of the pavement is needed, the repaving method of HIR is recommended so that an overlay may be placed on top of the recycled surface. Hot In-place Recycling is primarily used to correct distresses of pavement surfaces that are not caused by inadequacies in the pavement’s structure itself. Pavements that have been excessively patched, rutted, or chip-sealed are not prime candidates for HIR. Roadways that are being treated with Hot in Place Recycling must also have the structural strength to support the equipment weight. Additionally, the roadway must be wide enough for the equipment and have a base that is in good condition for HIR rehabilitation to be considered.
In comparison to other rehabilitation efforts, HIR is considered a more economical technique. Not only can it improve the frictional resistance of the surface and renew the overall surface, but it can also re-establish drainage and modify aggregate gradation. Engineers suggest Hot In-Place Recycling as a rehabilitation technique because it can be used to ensure the desired drainage capacity for the pavement. The HIR process allows for other treatment methods to be added on after its completion and disturbance to traffic is minimal. Other benefits include the extension of pavement life along with the improvement of ride quality. A new control system has also been developed in order to reduce gas emissions from the HIR equipment. This process is further explained here.
Hot In-place Recycling
COLD IN-PLACE RECYCLING (CIR OR CIPR):
Cold In-place Recycling is a rehabilitation technique that utilizes a milling machine in addition to a paver mixer. The purpose of the milling machine is to pulverize the top 2 to 4 inches of pavement and reduce this top layer of old pavement into finer particles. This process is completed without using heat to soften the surface, giving it its name–Cold In-place Recycling. Only a minimal total amount of heat is used throughout this process. After milling, the machine physically screens the material in order to provide the proper material size. The crushed material is then mixed in with recycling agents, such as emulsified asphalt or other stabilizers. If foamed asphalt is used as one of the stabilizers, then the CIR equipment must have a heating system that maintains the temperature for the asphalt to sustain its expansion ratio. After the addition of recycling agents, the new material is paved and compacted. Lastly, due to the high amount of voids produced from CIR, microsurfacing or a surface course such as a slurry seal is placed over the finished pavement. For roads with high volumes of traffic, an asphalt or concrete overlay is suggested.
Cold In Place Recycling
Like HIR, Cold In-place Recycling must only treat pavements that have adequate underlying structures. The thickness, age, and past pavement conditions must be examined prior to the rehabilitation procedure. The pavement age will help indicate the stiffness of the existing binder and help predict the quality of the structure. Softer and harder binders will affect the mix design for the CIR and call for different additives. If a geosynthetic interlayer is present within the current pavement, the recycled depth must reach the layer below the geosynthetic in order to completely remove it, or reach 1 inch above the geosynthetic to prevent its tearing. The cross-slope of the pavement along with its profile are improved with CIR. This rehabilitation technique is commonly used to treat pavement distresses such as rutting, fatigue, block cracking, raveling, potholes, and more. In cases where raveling occurs more frequently, a fog seal may be placed prior to the CIR surface. A pavement’s life span will extend 10 to 15 years using cold in place recycling. Since this process recycles the existing pavement, CIR is a form of treatment that is one of the most environmentally friendly techniques and reduces the rehabilitation costs of the pavement. Cold In-place Recycling not only conserves energy by using minimal heat throughout its process, but also reuses non-renewable resources, like aggregate and petroleum. Many roadways are paved with asphalt slurry which is composed of 5% asphalt cement; a material that is acquired from natural occurring petroleum. The remaining 95% is made up of aggregates. Therefore, by using a technique such as CIR, companies can lessen their dependence on further extractions of non-renewable resources such as petroleum thanks to the reuse and recycling of existing materials.
GEOSYNTHETICS:
One rehabilitation treatment that addresses the structure of the upper pavement is geosynthetics. Geosynthetics are man-made materials placed on the ground or pavement for pavement design purposes. The purpose of this treatment is to prevent moisture from seeping through underlying pavements and to reduce reflective cracking. Geosynthetics can help address lateral drainage, filtration, and reinforcement. Materials that are commonly used as geosynthetics are geogrids, membranes, composites, and fabrics/geotextiles. Geogrids will primarily slow occurrences of reflective cracking, but all other materials (membranes, composites, fabrics/geotextiles) will reduce reflective cracking and additionally provide a moisture barrier. As shown in the image below, geosynthetics are placed between the base and the subgrade, ensuring that the stresses are distributed and lowered at each point. The geosynthetic has a tensile stiffness that will limit strains placed on the base layers while increasing its shear strength. Additionally, the material will provide the pavement with a higher bearing capacity and will allow for support of larger wheel loads.
Two methods used for the design of flexible pavements reinforced with geosynthetics are the AASHTO Method and the National Cooperative Highway Research Program (NCHRP) Mechanistic-Empirical Method. As the AASHTO method is used to determine layer thickness, further calculations establish an understanding of the relationship between geosynthetic and layer thickness in order to design the preferred pavement performance. This method is site specific due to the materials and loads it is designed for. The NCHRP M-E method uses mechanistic properties of the pavement layers including strain response and material stiffness. Traffic load cycles and the Long Term Pavement Performance (LTPP) database are referred to in order to anticipate pavement failures. The approach is then applied to a geosynthetic-reinforced pavement. Both methodologies are complex and use predictions of the pavement performance, but the NCHRP M-E approach creates a basis of geosynthetic properties that is more consistent than the AASHTO approach. A more detailed description of each method’s approach is described in Geosynthetic-Reinforced Pavement Systems.
Geosynthetics Strain Response
FULL DEPTH RECLAMATION (FDR):
Another procedure that rehabilitates pavements is Full Depth Reclamation/Recycling, also known as FDR. Full Depth Reclamation is a method for in-place recycling. In order for deeper structural problems to be addressed, predetermined parts of the subgrade in addition to the base are uniformly pulverized. The asphalt’s full thickness is pulverized during this process and is blended with a portion of the underlying base to create homogenous material, as shown in the image below. This blended material then works as the new surface base. FDR ranges from 4 to 14 inches in depth but is primarily used to reach pavement depths of around 12 inches. During mix design procedures, the desired pavement thickness is determined. If the new desired thickness exceeds 6 inches, the FDR material must be placed and compacted in multiple layers.
In cases where FDR is not sufficient, engineers will stabilize the FDR material in order to increase the pavement’s strength capacity and shear strength, as well as to help control soil properties like the shrink-swell. This process is called Stabilized Full Depth Reclamation (SFDR). It includes the addition of mechanical, chemical, or bituminous stabilizers to the base and/or subgrade.
- Mechanical additives include: new aggregate, crushed portland cement concrete, or reclaimed asphalt pavement.
- Chemical additives include: lime, cement, cement kiln dust, lime kiln dust, fly ash, calcium chloride, and magnesium chloride.
- Bituminous additives include: emulsified asphalt, liquid asphalt, or foamed asphalt.
Stabilization may not be performed if the existing pavement includes geotextiles, if the underlying subgrade is too weak to withstand this process, or if the roadway has substantial amounts of grade changes. Many agencies opt for mechanical stabilization because it is more economical than chemical or bituminous stabilization. However, these stabilizers will result in even more flexibility and base strength. Importantly, the choice of stabilizing agent must be appropriately based on the properties of the aggregate material and their mix designs.
With FDR, the importation and exportation of pavement materials is reduced by up to 90% and this technique allows for traffic to return the same day. It is also a way to recycle all of the pavement materials, decrease greenhouse gas emissions, and minimize costs. If a roadway is expected to have an increase in vehicular traffic, this method is beneficial for rebuilding of the structural capacity. Full Depth Reclamation is able to treat all forms of pavement failures, even those of high severity. It is able to eliminate forms of cracking such as reflection, alligator, longitudinal, and transverse. Additionally, the grade of the pavement is contoured for improved surface drainage, which achieves lower water permeability. Contour grading designs the pavement in a way that directs water to designated areas while also preventing erosion and protecting vegetation. FDR has therefore become a prominent alternative to total reconstruction with road life extended up to 25 years.
FDR Schematic
FDR Machine
RUBBERIZED ASPHALT:
Rubberized asphalt is a rehabilitation method that provides a durable surface which increases pavement life. The materials used are hot mixed asphalt that is mixed in with crumb rubber; by doing so, the viscosity of the liquid asphalt is enhanced. Two processes commonly used to add the crumb rubber include the “field blend” and the “terminal blend”. Adding crumb rubber using the “field blend” ensures that the material is added to liquid asphalt prior to the addition and mixture of the aggregate; all of which take place at the asphalt plant. On the other hand, the “terminal blend” technique prepares for the crumb rubber to be dissolved into the liquid asphalt prior to the materials being exported to the asphalt plant.
This technique of using rubberized asphalt is most suitable for pavements that do not have structural issues or alligator cracking and are common for roads that need to be resurfaced or reconstructed. Using ultra-thin lift hot mix overlays will protect the underlying surface and extend pavement life. Water intrusion is also reduced along with various other surface irregularities. Similar to the process of hot-mixed asphalt concrete pavements, rubberized asphalt is placed using rollers and a paving machine. When roads are surfaced with rubberized asphalt the performance life can extend from 14 to 18 years.
Raw Rubberized Asphalt
Paved Rubberized Asphalt
RIGID PAVEMENT DESIGN
Rigid pavement refers to pavement constructed from cement concrete or reinforced cement concrete slabs. They are typically used for roadways that experience heavy traffic loads due to their high flexural strength. This means that rigid pavements will not deflect/deform very much when under high loads of stress. There are many types of rigid pavement, all of which have different purposes and uses. In the following paragraphs, we discuss the properties and characteristics of each type of rigid pavement
RIGID PAVEMENT TYPES
CONTINUOUSLY REINFORCED CONCRETE PAVEMENT (CRCP):
Continuously Reinforced Concrete Pavement (CRCP) is known for using reinforcement instead of transverse joints for crack control. Due to the use of reinforcement, CRCP is a more expensive option compared to the traditional jointed concrete pavement. However, the reinforcement provides improved long-term performance and requires less maintenance. The absence of joints also results in higher ride quality and thus, CRCPs are typically utilized in areas where high traffic volumes are expected. CRCP can be used for new construction and concrete overlays for roadways that have a traffic index in the glossary” href=”#traffic-index”>traffic index (TI) equal to or greater than 13.0. The traffic index (TI) is a measure of how much damage is done to the pavement from a single pass of a standard axle load over the expected lifespan of the pavement and is measured by the number of equivalent single axle loads (ESAL) it is expected to experience during its design life.
JOINTED PLAIN CONCRETE PAVEMENT (JPCP):
Jointed Plain Concrete Pavement (JPCP) is the most common type of rigid pavement. JPCP uses both longitudinal and transverse joints for crack control and is recommended for lower volume truck routes, ramps, and urban streets. Because this pavement does not require reinforcement and fabrication (as needed in Precast Concrete Pavement, PCP, discussed below), the costs for JPCP are lower initially. However, JPCP will require more maintenance, and will thus be less cost-effective over time.
PRECAST CONCRETE PAVEMENT (PCP):
The last type of rigid pavement is the Precast Concrete Pavement (PCP). PCP is a pavement type that uses panels prefabricated from off-site areas which are then delivered and transported for installation. Because PCPs are fabricated off-site, they require no curing time and once installed can be driven on the same day. Due to the shorter lane/street closure times, PCP is chosen over JPCP for areas that require shorter construction windows or for areas that have a high traffic volume. PCPs are also excellent choices for the long term and require little maintenance, however, are expensive due to fabrication costs.
Figure 621.1 taken from the Caltrans Manual compares the differences between a continuously reinforced concrete pavement (CRCP) and a jointed plain concrete pavement (JPCP).
Fig. 621.1 Types Of Rigid Pavement
TYPES OF CONCRETE
Concrete consists of three different types, and your choice depends upon your needs. The most standard type of concrete is Portland Cement Concrete (PCC), but there are others such as Rapid Strength Concrete (RSC) and Roller Compacted Concrete (RCC). Below we discuss the differences between these three types of concrete in detail.
As stated earlier, PCC is the most common type of concrete used. It is used in many applications such as new pavement, widening, reconstruction, and rehabilitation. It is composed of Portland cement (clay, limestone, shale), aggregate, water, and sometimes chemical admixtures. PCC is designed to last approximately 100 years or more if well maintained.
In cases where faster curing times are needed, Rapid Strength Concrete (RSC) is recommended. RSC is typically composed of PCC but with admixtures that highly accelerate the curing time or from a proprietary hydraulic cement that gains strength extremely quickly. It is most commonly used in areas that need to open to traffic quickly and is also used for JPCP replacements and repairs.
Roller Compacted Concrete (RCC) is made from the same materials as the conventional PCC, but with a lower water ratio. In other words, RCC is a drier mix that is stiff enough to be consolidated by vibratory rollers. RCC has similar characteristics to PCC with high strength, low maintenance, and long design life with quicker curing times than PCC. According to Caltrans High Design Manual, RCC is most commonly used on State highways for shoulders and temporary detours.
PAVEMENT JOINTS
Pavement joints are essential in most concrete installations because they help with preventing and controlling the formation of cracks. There are four types of joints: construction, contraction, isolation, and expansion. Construction joints are joints placed between two sections of concrete slabs, when concrete slabs are laid separately at different times. Contraction joints are joints that are sawed into new concrete slabs to regulate or control the location of random cracking that is caused by shrinkage, curling, and/or thermal cracking. Isolation joints are joints that are used to separate two adjacent concrete slab sections from columns or walls to allow for three-directional movement. In other words, isolation joints are used to separate or “isolate” a concrete slab from another object – typically a column. Lastly, expansion joints, also known as movement joints, are joints used with continuously reinforced concrete pavement (CRCP) to control cracking that occurs from thermal expansion and contraction. Below we provide pictures of each joint type, courtesy of Shuanglong Machinery.
Construction Joint
Contraction Joint
Isolation Joint
Expansion Joint
TRANSITION PANELS, TERMINAL JOINTS AND END ANCHORS
Transition panels are reinforced concrete panels that range about 12 feet long and are used at transverse joints of existing new asphalt and a concrete slab. These transition panels help reduce the faulting distresses and deterioration of the joint where rigid and flexible pavements join together. Concrete pavement transition panels also provide a smoother ride quality as they minimize distortion of asphalt at the location of the joint. Figure 622.5A is taken from Caltrans Highway Manual and shows the concrete pavement to asphalt pavement transition panel.
Figure 622.5A: Concrete Pavement to Asphalt Pavement Transition Panel
CONTINUOUSLY REINFORCED CONCRETE PAVEMENT TERMINAL JOINT TYPES
As mentioned above, Continuously Reinforced Concrete Pavement (CRCP) are concrete pavements that use reinforcement instead of transverse joints to control cracking. However, when transitioning from rigid pavements to a different pavement type, terminal joints are required. The different terminal joints types and their purposes are listed below and are taken directly from the Caltrans Highway Design Manual. Figure 622.5B shows the design of an expansion terminal joint system between CRCP and a structure approach slab.
- TERMINAL JOINTS TYPE (A) – Use when constructing new CRCP next to existing asphalt pavement and if a concrete pavement transition panel is not viable.
- TERMINAL JOINTS TYPE (B) – Use when the newly constructed CRCP terminates at future pavement construction.
- TERMINAL JOINTS TYPE (C) – Use when the newly constructed CRCP terminates at a proposed temporary asphalt pavement construction for traffic staging.
- TERMINAL JOINTS TYPE (F) – Use when constructing new CRCP next to a structure approach slab.
- TERMINAL JOINTS TYPE (G) – Use when constructing new CRCP next to new or existing JPCP, PCP, or existing CRCP.
- EXPANSION TERMINAL JOINTS SYSTEM (ETJS) – ETJS is a series of two 14-ft reinforced slabs with two full depth, full-width transverse expansion joints designed to absorb the pavement expansion without damaging adjacent structures. For CRCP, expansion terminal joint system (ETJS) shall be used at all transitions to or from structure approach slabs whereas terminal joint type G shall be used at all transitions with another pavement.
Figure 622.5B: Expansion Joint System Between CRCP and Structure Approach Slab
JOINTED PLAIN CONCRETE PAVEMENT
Jointed Plain Concrete Pavement (JPCP) also utilizes two different types of terminal joint when installing JPCP adjacent to existing concrete pavement, structure approach slab, or asphalt transition panel. Terminal Joint Type 1 is used when laying new JPCP next to existing rigid pavements or structure approach slab and utilizes a transverse construction joint and dowel bars. Dowel bars are rebars or short steel bars that are drilled into the existing concrete pavement to bond and connect concrete slabs. On the other hand, Terminal Joint Type 2 is used when constructing new JPCP to an asphalt transition panel. The terminal joint type 2 also consists of transverse construction joints and a dowel bar which is installed at the joint of new concrete pavement and new concrete.
JOINT SEALS
Joint seals are sealants that are applied in the joints or between concrete slabs and transitions to minimize water infiltration and penetration of incompressible materials through the joint. Joint and crack seals are used to protect wide joints (3/8 inch or wider) rather than narrow joints. According to Caltrans Highway Design Manual, joint sealants are not required for new construction, widening, or for reconstruction except when the joints are: isolation joints, expansion joints, longitudinal construction joints in all desert and mountain climate regions, or transverse joints in JPCP in all desert and mountain climate regions.
Depending on the type of joint sealants used, joint sealants generally have an effective lifespan of 10-15 years. When the joint sealants have deteriorated due to erosion and sun damage, they should be replaced as required to ensure the longevity of the pavement. Joint seals should also be replaced whenever there is maintenance, rehabilitation, or construction work for any dowel bars that need to be replaced and/or retrofitted. For areas that do not have joint sealants applied between slabs/pavement, consult your engineer or city and local state to determine if sealant application is necessary.
Joint sealant types vary depending on different criteria and usage. Listed below are the criteria parameters for selecting the proper joint seal material:
- Project Environment
- Type of Roadway
- Condition of Existing Reservoir
- Expected Performance
- Cost-Effectiveness
DOWELS AND TIE BARS
Dowel bars are smooth steel bars that are used as load transfer devices to reinforce cracks in highway pavement. Dowel bars shall be placed within the traveled way pavement structure at the following joints:
- All transverse terminal joints in CRCP at new and existing JPCP or structure approach slabs.
- All transverse contraction and construction joints in JPCP.
- All transverse construction joints in PCP.
- All transverse transition joints regardless of concrete pavement type where concrete pavement abuts to structure approach slabs or other concrete pavement type.
Tie bars, on the other hand, are deformed rebars that are used to connect the face of rigid slabs together to prevent transverse cracks, deflection and lane separation. Tie bars are not used as a load transfer device and therefore should not be used when considering street widening.
Tie bars shall be placed at longitudinal joints except at the following locations:
- Adjacent concrete pavement when the spacing of transverse joints of adjacent slabs is not the same.
- Roller compacted concrete.
- Do not tie more than 50 feet width of JPCP together to preclude random longitudinal cracks from occurring due to the pavement acting as one large rigid slab. In order to maintain some load transfer across the longitudinal joint, the Standard Plans include details for placing dowel bars in the longitudinal joint within the travelled way for this situation.
- Individual slab replacements.
BASE INTERLAYER
Base interlayers are primarily used to prevent the spreading of cracks in pavement. They are a geotextile fabric that functions as a moisture barrier as well as a reflective cracking mitigation measure and is placed between a lean concrete base and asphalt layer.
TEXTURING
Texturing refers to the pavement finish surfaces. Texturing is an important component in rigid pavement design as it plays a role in roadway safety and noise control. By applying a surface finish to the pavement, it will increase the amount of friction and traction between tires and the roadway surface, but it will also increase noise pollution. It is important to find a fine balance between the two when considering the depth of “grooving” wanted for your roadways.
PAVEMENT SMOOTHNESS
Along with pavement surface texture, pavement smoothness is an important factor in the design of rigid pavements. Smoother pavements provide improved ride quality, extended pavement life, reduced highway travel user costs, lower pavement maintenance costs, less work zone activities, and reduced noise pollution. Pavement smoothness, or ride quality, is measured in terms of the International Roughness Index (IRI). For new construction, reconstruction or widening/lane replacement projects, the concrete pavement is engineered and built to have an IRI. Finding the balance between smoothness and roughness of the road is determined by the load, amount of traffic, type of traffic, and climate conditions.
PROCEDURES FOR NEW, WIDENING, AND RECONSTRUCTION PROJECTS
For any roadway project, the first item of importance when designing a new roadway is it’s soil type and bearing capacity. This information will reveal whether the soil is suitable to function as a subbase for your road or highway. If not, the existing subgrade will need to be treated or removed and replaced with suitable fill. Once this has been determined, the climate region will determine what type of design measures are needed for the roadway (i.e. depending on the amount of rainfall an area receives annually, it is imperative to design proper drainage facilities and flood control measures). Depending on the climate region, soil type, and whether the pavement has lateral support or not, a table from the Caltrans Highway Design Manual (Table 623.1) can be used to determine the pavement layer depths. Once this is done, selecting the pavement structure layers and choosing their depth is the final step of the design process. Figure 623.1, a design tree from the Caltrans Highway Design Manual is provided below; and tables and relevant information can be found in section 623 of the manual for pavement design.
Figure 623.1: Rigid Pavement Catalog Decision Tree
ENGINEERING PROCEDURES FOR PAVEMENT PRESERVATION
Understanding procedures for maintenance and pavement preservation are equally important in the design of your pavement to maximize the longevity of your roadway. Knowing when to seal random cracks to prevent water infiltration, implementing a dowel bar retrofit for street widening or slab replacements, grinding or grooving to restore surface texture, and when to apply special surface treatments (typically for asphalt pavements, such as a slurry or fog seal) will help extend your pavement design life and reduce extra costs on maintenance and repairs down the line.
RIGID PAVEMENT REHABILITATION
After some time, rigid pavements will require major rehabilitation such as a concrete overlay, lane replacement, or asphalt overlay. In this case, it is important to reach out to a licensed Professional Engineer to examine the severity of the distress and determine the level of rehabilitation required. The selection for the appropriate repairs needed will be determined by the roadway’s life-cycle cost analysis, load transfer efficiency to the joints, materials testing, ride quality, safety, maintainability, constructability, and visual inspection of pavement distresses.
PROCESS OVERVIEW
Listed below is an overview of the complete roadway construction process. We discuss the details of the design process in the sections that follow.
- Determine the project type. The Earthbag Village will be a new development and therefore falls under “new construction”. Other types of construction could be widening (adding additional lanes to increase capacity and improve traffic flow), pavement preservation (including preventive maintenance to preserve adequate pavements condition and capital preventive maintenance program for short-term repair projects), roadway rehabilitation (returning distress roadways to adequate condition), reconstruction (replacing old pavements and rebuilding roadside features), temporary pavements and detours (temporarily carrying traffic during construction process), and stage construction (applying multiple layers to flexible and rigid pavements to increase pavements thickness).
- Acquire zoning and property information based on the project location’s specific zoning laws and regulations. For instance, if the property falls under an Environmentally Sensitive Habitat Area (ESHA), there will be more development limitations for the purpose of ecosystem protection requirements. Always make sure to check in with the Department for Construction Services in advance so that you are aware of and can account for these potential limitations.
- Design your project with the collected data, documentation, and technical reports. Follow code and regulations required for the design of the project and make corrections until the design meets all standards. Specifically, for this project, we are designing the pavement for the roadway within the Earthbag Village as well as the central pathways, so it is recommended to follow pavement design code such as AASHTO (American Association of State Highway and Transportation Officials) guidelines, Americans with Disabilities Act (ADA) compliance standards, and fire department access regulations.
- Submit your plans for approval, acquire permits. If the plans are not approved, make the necessary corrections and resubmit until the plans are approved by your local or state building and safety department.
- Find a contractor who is suitable for the job and within your budget. The appropriate contractor should be chosen from a pool of potential candidates that have submitted a bid. Interviews are strongly recommended in the selection process, with requests to check each contractor’s licenses, complaint, references, and litigation history. Carefully read each section of your contract, negotiate, set rules, and verify their insurance before proceeding further.
- Construction begins. During several stages/phases within the project make sure to meet and pass inspections by the city or state to ensure the project follows the approved plans, codes, and standards.
- Pass the final inspection and receive a certificate of occupancy.
PREPARING A PAVEMENT RECOMMENDATION
A Professional Engineer (PE) prepares a pavement recommendation to further describe the most efficient pavement alternative. The documentations, which vary depending on the scope of each project, will include cost analysis, advantages and disadvantages of each option, and city minimum requirements.
Appropriate data, documentation, information (such as the project site), geotechnical parameters, and the year-round climate of the project location must be submitted for the project manager to decide the best pavement plan. Next, the project engineer must ensure the feasible pavement alternatives all satisfy the minimum design standards. All options must comply with the Public Resources Code (Section 42703) concerning alternatives to Rubberized Hot Mix Asphalt (RHMA). The project engineer then summarizes the essential details of the project, references the resources used in research, and obtains engineering stamped approvals.
Important resources include the AASHTO “Guide for Design of Pavement Structures”, a geotechnical report, climate data, and life cycle cost analysis (LCCA). The list of documentation for pavement design is listed below.
DOCUMENTATIONS FOR PAVEMENT DESIGN:
- Pavement design life with construction year and design year
- The Unified Soil Classification of the subgrade soil and the California R-value
- The strength properties and characteristics of base and subbase materials
- Ride quality data as measured by International Roughness Index (IRI)
- The Traffic Index (TI) and equivalent single axle loads (ESALs) or spectra used to engineer each pavement structure
- Life-cycle cost analysis (LCCA)
PROJECT SPECIFIC CONDITIONS TO CONSIDER
Project-specific conditions must be considered before choosing road and walkway pavement choice(s). The various types of considerations are listed and discussed below.
PAVEMENT DESIGN LIFE
Design life is one of the most vital considerations for a pavement design project. It is defined as the time period in which newly constructed or rehabilitated pavement is engineered. For heavily trafficked roads, a long-term design life for pavements will be required to ensure maximum efficiency of the selected pavement. Temporary roads and parking lot pavements can be designed with shorter design lives, which can help to save more time, money and resources.
TRAFFIC CONSIDERATIONS
It is important to determine the types of traffic loadings for adequate pavement design. Below is the procedure for traffic loading determination:
- Estimate projected truck traffic volume for the different truck and transit vehicle types by axle classification: Figure C-1 provided by the Federal Highway Administration shows the different vehicle category classifications.
- Convert the projected truck traffic data into 18-kip equivalent single axle loads (ESALs): In the Alaska Flexible Pavement Design Manual, section 6.3 explains in detail the calculation process for equivalent single axle loads ESALs with examples.
- Determine the Lane Distribution Factor: On multilane highways, there are different types of vehicle that participate in the traffic, varying by lanes, including passenger cars, pickups, vans, and buses generally in the median and high-occupancy vehicle (HOV) lanes, and heavy trucks in the outside lanes. Due to this fact, the distribution of truck/bus traffic by lanes must be considered in the engineering design process for all multilane facilities to ensure that traffic loads are adequately distributed. Because of the uncertainties and the variability of lane distribution of trucks on multi lane freeways and expressways, statewide lane distribution factors have been established for pavement engineering of highway facilities in California.
- Convert the total projected ESALs into a Traffic Index (TI) to determine minimum pavement thickness.
TI = Traffic Index for a given design life
ESAL = Total number of cumulative 18-kip Equivalent Single Axle Loads for all truck/bus types over the design life of the pavement structure
LDF = Lane Distribution Factor
In the Highway Design Manual, section 613.3 (Traffic Index Calculation) provides more insight and details into the topic.
SOILS CHARACTERISTICS
In any site development project, soil characteristics analysis is required to prepare for the geotechnical report. Soil analysis will disclose if the soil type is suitable for the construction. It also determines the soil’s bearing capacity, strength, density, as well as its ability to support the applied loads. The analysis also aids to determine the appropriate foundation to properly support the loadings. The classification of soils is reported with the Unified Soil Classification System (USCS) from ASTM D 2487. The report also includes the California R-Value which identifies the climate of the site location. Suitable soils can be imported for cases such as imported borrow, compaction, fill, or remove and recompact.
CLIMATE – DETERMINE THE CLIMATE REGION
Climate conditions are an imperative aspect in determining the optimal type of pavement for the project. There are several factors that can contribute to the deformations of the pavement, including solar radiation, precipitation, temperature, freezing, thawing. Heavy precipitation can result in increased sediment erosion and water seepage into base and subbase, weakening the layers. The figures below illustrates various climate regions in California and Utah. More information concerning other regions of the US can be found here.
Fig. 615.1 Climate Zone Information for the State of California
Climate Zone Information for the State of Utah
EXISTING PAVEMENT TYPE AND CONDITION
It is important to review the existing pavement type and condition. Some crucial factors are listed below:
- Type of pavement on adjacent lanes or facilities.
- Similar pavements performance and condition in the site location.
- Corridor continuity – Verifying whether the corridor pavement material type or treatment and lane width is continuous or varying throughout the length of the corridor.
- Maintaining or changing grade profile.
- Existing pavement widening with a similar material.
- Existing pertinent features, such as curbs and dikes, drainage facilities, lateral and overhead clearances, median barriers, and structures which may create some restrictions on pavement structure.
RECYCLING AND AVAILABILITY OF MATERIALS – MATERIALS REPORT
Sustainability is one of the main considerations for One Community projects, therefore, it is vital to search for local suitable materials and reduce the use of engine-based machines (enginery). Minimizing the use of enginery will lead to better efficiency of resources, time and money. Existing pavement can be reused by crushing the aggregate for the new asphalt or concrete pavement. This can solve the problem of lacking available materials for construction. In addition, recycling pavement can be a reasonable alternative to 100% new flexible pavement. Project engineers must examine performance experience, material properties, project cost, and use engineering judgement when deciding to utilize the recycled materials. Inappropriate placement of recycled materials during construction can also adversely affect local water systems, so it is important to determine Best Management Practices (BMPs) to reduce the risk of potential stormwater pollution.
MAINTAINABILITY AND CONSTRUCTABILITY
Maintainability is defined as the ability of building or restoring highway facilities in a timely and cost-effective way. This includes minimal traffic exposure to the workers and minimal traffic delays to the traveling public. On the other hand, constructability considers all the factors potentially impacting construction of the project. These considerations include pavement type, location specific concerns, safety concerns, etc.
Matters concerning construction that influence pavement type selection include: size and complexity of the project, stage construction, lane closure requirements, traffic control, safety during construction, time constraints, adequate work area, and other constructability issues that have potential of generating contract change orders. Other constructability items that should be addressed in the project include:
- Providing clearance widths for paving machines to barriers along with hinge points to ensure better control of smoothness and paving operations.
- Establishing access for construction equipment and delivery trucks. The constant delivery of materials is essential for the operation of paving machines at consistent rates. Additionally, this ensures the construction of smooth and long-lasting pavements.
- Safety and convenience for the public.
- Utilizing thin layers of different materials for the preservation of resources such as time and cost, as opposed to thick layers composed of single materials.
- Taking into account the impact on the pavement’s long-term performance or maintenance due to combined lifts of various materials.
- Considering the distance of the construction site to the material batch plant.
- Providing consistent paving operations through the maximization of lane closure times or the utilization of detours.
- Efficiently scheduling the order of tasks to ensure smooth and sturdy pavements.
LIFE-CYCLE COST ANALYSIS AND ASSESSMENT
Life-Cycle Cost Analysis (LCCA) consists of an economic analysis that compares initial cost, future cost, and user delay cost for various pavement alternatives. LCCA plays an integral role in the decision making process for the selection of pavement type and design strategy. This can be used to compare life-cycle costs for different pavement types, rehabilitation strategies, and pavement design lives.
The basic formula used to calculate Life-Cycle Cost is listed below:
Basic Formula for Calculating Life-Cycle Cost
ROADWAYS DRAINAGE AND COLLECTION
PURPOSE OF ROAD DRAINAGE
Roadway drainage is the removal of stormwater runoff from the road and the conveyance of runoff from the upstream location to outlet towards a downstream location. Every roadway project should provide a drainage plan for the collection, transport, and discharge of stormwater runoff away from the roadway to promote safety of its passengers and flood management. Other roadway drainage purposes include property damage prevention, erosion and sediment pollution prevention, and increased pavement life.
The development of the site and roadways is planned for a county that did not offer a drainage design manual. Because of this, we chose to use the standards from both the San Diego Drainage Design Manual and Park City Drainage Manual. Both drainage manuals utilize the rational method and common hydrology equations to solve for peak flow. Between the two, the San Diego Drainage Manual goes into more depth with hydrology equations, erosion control best management practices, and drainage design criteria. Even so, because the development of the site will take place in a different and colder location, it is important to take into account cold climate hydrology calculations, such as snowmelt runoff calculations. Thus, we refer to Park City’s Drainage Manual for cold climate hydrology criteria. Although both criterias are discussed in detail, we highly recommend that you check with your municipality’s current drainage standards before considering moving forward with the standards given below.
Please note that anything followed by an asterisk (*) implies that the standards are taken from the San Diego Drainage Manual. Always double check that these standards meet your local and state minimum code and requirements before moving forward with any project planning and design.
GETTING STARTED
To get started, items we will need to prepare include:
- Drainage Report – The drainage report must show:
- Proposed drainage conditions.
- Existing drainage conditions at the time of plan approval.
- A complete plan set, which contains.
- Hydrology studies, hydraulic design – for 1000-year storm event.
- Plan profile plots.
- Existing and proposed drainage facilities.
- Sediment analysis.
- Any other relevant plans or documentation required by your local or state guidelines.
- Storm Water Quality Management Plan (SWQMP) – for 1000-year storm event.
- A Hydrology study or report will help determine the design runoff discharge that the project will have to plan for. The peak discharge for a storm event is dependent upon many factors such as the intensity of the rainfall, storm frequency, drainage area, ground cover or surface type, slope, and soil type.
ROADWAY DRAINAGE CRITERIA
The criteria for designing for roadway drainage is to determine the peak flow and design the conveyance and inlet system to handle the capacity of the storm. Other roadway drainage requirements include:*
- Maximum allowable drainage on any street section shall be based on gutter flow (please see gutter flow section below).
- Street drainage shall be intercepted with an underground storm drain prior to any street grade of ten percent (10%) or greater.
- Design for drainage on any multi-lane street section shall require retention of the drainage flows in such a manner that one lane in each direction of traffic will be clear of flow at all times for a 50-year (minimum) frequency storm.
- The minimum street and gutter grade permitted is 0.6 percent.
- All streets shall have a nominal two percent (2%) crown unless superelevated. (The crown of the street is the center crest of the street where a 2% grade is applied away from the center to promote flow from the center of the road to the gutters or shoulders).
INLET LOCATIONS
Storm drain inlets are catch basins that collect storm water to channel it through a storm drain conveyance system. It is important to strategically place storm drain inlets in specific locations to protect the safety of the public and prevent flooding. According to the San Diego Drainage Manual, mandatory inlet locations include:*
- Locations where flow in roadway cross-section exceeds the limitations (given in the roadway drainage criteria above).
- Low points (sags and sumps) in a roadway profile.
- The upstream side of superelevated roadway cross-sections (located in a manner such that no more than 0.1 acre contributes to flow crossing traffic lanes).
- Superelevated roadway transition sections where concentrated flows are not permitted to cross traveled lanes under the design storm frequency for the street. Median inlets shall be designed and spaced so the lane adjacent to the median (number one lane or fast lane of traffic adjacent to the median) is free from drainage flow for the design storm frequency. (Whenever a vehicular travels along a curved path or roadway it experiences centrifugal force. Superelevation is a transverse slope on a roadway that utilizes centrifugal force to reduce the chances of a vehicle to overturn and/or skid by raising the outer edge of the road on the curve in respect to the inner edge).
- Tee intersections where the terminating or side street grade exceeds five percent (5%) or for flatter grades when the gutter flow will encroach or overrun the cross gutter.
- Subdivision boundaries (for flows in the public right-of-way).
- Intersections where flow is directed towards the intersection without relief from a cross gutter.
Other recommended inlet location additions may be prescribed in locations where there is a change in the roadway cross-slope and/or when there is a change in the downstream roadway longitudinal slope. These are common locations where sedimentation build-up can occur, and therefore installing inlets in these areas will help improve the functionality of the storm drain system as well as increase the safety of its drivers.
The criteria and sizing of the inlet is determined by the storm event it was designed for. In other words, the inlet must be sized to accept and convey one hundred percent (100%) of the storm water runoff that it receives. Storm water inlets must also be designed so that the energy gradient (amount of energy in the water spread over a distance – the energy consists of pressure, velocity, and elevation) is a minimum of six (6) inches below the grade of the gutter or grate of the inlet. Depending on the type of inlet used (i.e. grated inlets, slotted inlets, combination inlets, etc), there are specific procedures to determine the capacity of runoff it can intake. Standard Drawings for the type of inlet and/or when the inlet is required can be found on the City of San Diego’s website under standard drawings.*
GUTTER FLOW
Figure: 3.3 Gutter and Roadway Discharge-Velocity Chart (8” Curb)
Gutter flow is flow collected from stormwater runoff from a site, property, and roadway that runs parallel to the street and into a storm drain. Most gutter flow discharge capacity is designed with the following assumptions:
- Uniform flow (flow with a constant velocity/speed)
- Six to eight-inch curb heights
- Standard gutter widths (5 to 6 inches)
- Two percent (2%) cross-slope
With the velocity of the flow, one can determine the amount of runoff that the gutter will convey. The “n-value” is Manning’s n, which is a coefficient that represents the roughness/friction applied to the flow from the channel.
STORM DRAINS
Storm drains are generally underground conduits that convey flow and surface drainage to manage flooding during storm events. As a rule of thumb, the storm water system must be able to handle the peak discharge (the maximum rate of flow during a storm event) that it was designed for without affecting any adjacent property. As stated earlier, the peak discharge is determined by the hydrology study, and is dependent upon the maximum flow width, depth, and velocity. In order to protect public safety and reduce the risk of flooding, storm drain systems are often installed underground.
STORM DRAIN DESIGN
The design criteria for a storm drain is listed below:**
- Storm drains must have the capacity to convey the peak discharge for the design storm frequency.
- Storm drains systems will convey the design flow with a minimum freeboard of 1 foot below the ground surface or gutter elevation.
- Storm drains that drain the public right-of-way must be a minimum of 18 inches in diameter.
- Diversion or the separation of drainage flow is not allowed. (You cannot set multiple discharge points and inlet locations must be contained within the same watershed area).
- Storm drain conduits/systems and sanitary sewer lines must have a minimum horizontal clearance of ten feet (10’) (outside diameter to outside diameter) and five feet (5’) (outside diameter to outside diameter) from potable water lines, reclaimed water lines, and other storm drains.
- A minimum of one foot (1’) vertical clearance (outside diameter to outside diameter) between the storm drain system and other underground utilities must be maintained.
- The minimum ground/surface cover for a storm drain system is dependent upon the storm drain material type and strength, size of conduit, cover material, bedding conditions, and traffic loading. It is the designer’s responsibility to determine the requirements needed to uphold the safety of the public and reduce damage to adjacent property. Typically maintaining a minimum soil cover of two feet (2’) or one foot (1’) below pavement subgrades, whichever is greater, is the general rule of thumb.
- The minimum pipe grade of the pipe shall be 0.5%, have a minimum velocity of 4 feet per second (4 FPS), and the pipe must be running a quarter full. Flatter grades may be approved by the city if there are no other practical solutions available.
- Pipes must be designed to flow full and free of pressure heads, except for sudden grade changes where a small pressure head cannot be avoided.
**The design criteria and standards are meant for storm drain conduits with a circular cross-section. Other cross-sectional shapes can be calculated by the design engineer using Manning’s equation for pipe flow.
CLEANOUTS
Cleanouts are structures that provide access to a main drainage or sewer system for maintenance purposes. When designing a storm drain system, it is important to specify where cleanouts will be located and how far apart they will be spaced. A table listing a range of pipe sizes and respective maximum cleanout spacing is given below:*
Table 4.1 Maximum Cleanout Spacing
Cleanouts must also be located as follows:*
- At the end of all horizontal curves in the conduit while maintaining maximum spacing.
- At the Point of Compound Curvature (PCC) and/or Point of Reverse Curvature (PRC) of curves; [The PCC is location where two curves of different angles and radius are connected and the PRC is the location where two roads or pathways cross and curve in opposite directions.]
- At all horizontal angle points, except a single horizontal angle point of 10 degrees or less in cases where:
- The angle point does not combine a horizontal and vertical curve.
- The angle point is located within forty feet (40’) of another cleanout or outfall.
- Abrase bed load materials, under relatively high velocities (15 FPS or greater) will not occur.
- Typically on sag vertical curves, the cleanout should be located at the end connecting the flattest grade.
- All vertical angle points except:
- A single vertical angle point of 10 degrees or less in cases where;
- The angle point does not connect a horizontal and vertical curve.
- The angle point is located within 10 feet of another cleanout or outfall.
- Abrasive bed load materials, under relatively high velocities (15 FPS or greater) will not occur.
- A single angle deflection of 30 degrees within ten feet (10’) of an outfall may be approved, provided a factory manufactured elbow (10 degrees maximum angle points) is used. Should the conduit ever be extended from this outfall, a cleanout shall be provided at this point. Should the direction of the pipe change more than a total of 30 degrees in the vertical or horizontal direction from the top of slope to bottom of slope, a cleanout is required at the bottom angle point.
- A single vertical angle point of 10 degrees or less in cases where;
EASEMENTS FOR ROADWAY STORM DRAIN DESIGN
Easements are legal rights that allow, limit, or give access to private property for exclusive use such as utility maintenance & repairs and fire access. The minimum easement width required for subsurface stormwater conveyance systems is provided in Table 4-2 given below.
Table 4-2: Minimum Easement Widths
Table 4-2 assumes that the storm water drain pipe is installed in the conventional manner, meaning the pipe will have a maximum cover of 15 feet from the top of the pipe outside diameter (O.D.). In the case that the storm drain pipe cover falls between 15 and 25 feet, two additional feet (2’) of easement width will be required for every additional foot over 15 feet. When storm drain covers exceed 25 feet, City consultation and approval along with special additional easements are required.
All storm drain easements and structures must be physically accessible from the public right-of-way. In other words, the permanent structural improvements and developments cannot be built directly over a storm drain easement. Some exemptions for facilities such as parking lots, recreation fields and trails, maintenance access roads, and fencing may be allowed at the approval and permission of the local or state building department. In cases where existing permanent structures are located on a storm drain easement, the storm drain easement may be relocated to another location at the discretion and approval of the local or state building department. The costs associated with the relocation of the storm drain will fall on the requesting party or client.
Storm drains must also have an additional minimum easement of five feet (5’) from the edge of building foundations (non-commercial or industrial) to reduce the potential surcharge effects (adjacent loading impacts) that the building foundations can induce on the storm drain. If a structure exists on both sides of the storm drain, an additional easement of ten feet (10’) on both sides of the storm drain outside diameter (O.D.) is required. Easements located adjacent to commercial or industrial property, apartment or condominium apartments, private streets or driveways, and complexes that require vehicular access require a minimum easement of twenty feet (20’) width and the entire width of the easement must be paved.
When storm drains are located near slopes, buildings, or retaining walls, the local or state building department will require a submittal by a registered Professional Civil or Structural Engineer (PE, SE) with design calculations showing that there will be no adverse effects or loading on the storm drain. The design calculations must also show that during trenching operations for maintenance and repairs to the storm drain, any adverse loading from the slopes, building, or retaining wall must not fall within the area of influence of the storm drain.
Access roads must be provided to all storm drain manholes, cleanouts, outfalls, etc. The access roads must be:
- A minimum of fifteen feet (15’) wide.
- Have a maximum grade of 4%.
- Have a minimum two hundred foot (200’) transition prior to meeting the maximum 4% grade.
- Must be widened to a minimum of twenty feet (20’ – a 5’ increase from the minimum width of 15’ as given in the bullet point above), when the access road falls within twenty-four feet (24’) radius from storm drain appurtenances (manhole, cleanout, outfalls, etc).
- If the access road is designed for multiple uses (pedestrian walkway, vehicular access), it must have a minimum width of 24 feet.
WATERTIGHT JOINTS
Watertight joints are gaskets that prevent the infiltration or exfiltration of soils, contaminants, and liquids in a storm drain. Water tight joints on a storm drain are required in situations and locations where:
- The hydraulic grade line (HGL), which is the pressure and elevation energy of water, is greater than 5 feet of the inside crown of the pipe, for more than 40 feet of pipe length.
- Where the grade of the pipe exceeds 20%.
- In areas where groundwater levels may potentially rise higher than the invert elevation (the pipe’s inside diameter lowest elevation point) of the pipe.
SLOPE DRAINS
Slope drains are conduits that have a grade of 20% or higher and are implemented when discharging flow to an outlet nearest a well-defined natural drainage channel that has the capacity to convey the discharge. Sometimes, the cost of extending the slope drain to the outlet can be very expensive due to the 20% grade requirement. If the costs are increased substantially to meet this requirement, the outlet may be moved to the slope face if the calculated velocity does not exceed the Maximum Permissible Average Velocity for natural drainage channels given by the local or state requirements. Other requirements include*:
- Slope drains may be permanent or temporary structures that can be utilized for future extension of permanent installations, above or below the surface.
- Slope drains must be concealed by burial or other means if they are placed in landscaped areas or if they pose as an obstruction and/or distraction.
- Slope drains must have a service life of 100 years.***
- Slope drains must have watertight joint connections.
- Proper anchorage or cutoff walls must be installed in intervals of a maximum of 30 feet of conduit with slopes of 3:1 (H:V) or higher—metal or fiberglass cutoffs are not allowed.
- All slope drains located on the surface require special approval by the municipality.
- Reinforced masonry or reinforced cast in place concrete cutoff walls is required.
- Cleanouts for slope drains are to be half benched. When cleanouts are designed to be half-benched, this refers to the lower half of the pipe extending through the cleanout. The upper half remains open should there be any maintenance needs at the cleanout.
*** Storm drains must have a minimum design life of at least 60 years. A minimum of 100 years design life must be met in the following conditions described in Pipe Design Life.
PIPE DESIGN LIFE
As stated earlier, storm drains must have a minimum design life of 60 years. A storm drain must have a 100 year design life when:
- The height of a cover (manhole or cleanout) exceeds 15 feet.
- The storm drain conduit is located under a structure or overhang of a structure that has been permitted with an Encroachment Maintenance and Removal Agreement (EMRA).
- The storm drain conduit is located within a major, prime, arterial or collector street.
- The conduit is located in between or adjacent to structures that are a distance equal to or less than the vertical pipe cover depth (from the structure to the center of the pipe).
- Any storm drain is under a pressure head (pressure energy measured in feet).
- It is a slope drain.
STORM DRAIN PLANS
When submitting Storm Drain Plans for design and construction, it must include the following*:
- Plan and profile for all public storm drains showing all cleanouts, inlets, and catch basins with their respective invert elevations, rim elevations, type, and station.
- Stationing shall increase in the up-grade direction from the lower end of the storm drain.
- Stationing is a form of measurement that is commonly used in surveying and engineering to reference the distance between different points. One (1) station is equivalent to 100 feet and is written in the following format: 1+00 STA.
- Hydraulic Grade Line (HGL) of the flow within the pipe, including hydraulic jumps.
- Design flow and velocity (I50-year, or 100-year, as appropriate).
- Pipe design load rating or equivalent information (depending on pipe material, this might include pipe gauge or wall thickness).
- Flow and velocity at the outfall of the pipe.
- Flow capacity of the pipe (Qpipe).
- Length, material, and diameter of all storm drains.
- Property lines, right-of-way limits, street names and widths, finished grade.
- Conflicting underground utilities.
- Drawing numbers for related easements and existing structures.
- Delineation of the drainage basin for the storm drain that includes area calculation.
CONSIDERATIONS FOR QUALITY DRAINAGE DESIGN
- Safety
- Convenience
- Aesthetics
- Flooding prevention
- Subgrade infiltration
- Erosion and pollution prevention
- Cost of construction
- Cost of maintenance
STANDARD HIGHWAY DESIGN FEATURES
- Dikes
- Curbs
- Gutters
- Median drains
- Roadside ditches
- Overside drains
- Drop inlets
- Storm drains
HYDROPLANING CONSIDERATIONS
- Prevent Sheet Flow:
- Maximize transverse slope.
- Maximize pavement roughness.
- Use of graded course.
- Gutter Flow:
- Limit water spread.
- Maximize interception of gutter flow above superelevation transitions.
- Sag Areas:
- Limit pond duration and depth.
- Overtopping:
- Use appropriate freeboard and/or headwater elevation.
ROADSIDE DRAINAGE
- Median Drainage:
- Drainage across the median: Slotted drains should be used to intercept sheet flow.
- Grade and Cross Slope:
- To find the correct grade for your road you need to refer to section 305.2 of the HDM and 405.5 for the cross slope.
- Erosion:
- Provisions for erosion control should be provided when velocities for soils are excessive.
- Asphalt or concrete ditch paving may be required for severe conditions; if conditions are less severe ground cover can be used as a solution.
- Economy in Design.
The roadway drainage requirements include the following:
- Maximum allowable drainage on any street section shall be based on Section 3.2.
- Street drainage shall be intercepted with an underground storm drain prior to any street grade of ten percent (10%) or greater.
- Design for drainage on any multi-lane street section shall require retention of the drainage flows in such a manner that one lane in each direction of traffic will be clear of flow at all times for a 50-year frequency storm.
- The minimum street and gutter grade permitted is 0.6 percent.
- All streets shall have a nominal two percent (2%) crown unless superelevated.
STORM DRAINAGE
Storm drain plans shall provide a minimum amount of information regarding storm drain design and construction, including all of the following:
- Plan and profile for all public storm drains showing all cleanouts, inlets, and catch basins with their respective invert elevations, rim elevations, type, and station.
- Stationing, which shall increase in the up-grade direction from the lower end of the storm drain.
- Hydraulic Grade Line (HGL) of the flow within the pipe, including hydraulic jumps.
- Design flow and velocity (50-year, or 100-year, as appropriate).
- Pipe design load rating or equivalent information (depending on pipe material, this might include pipe gauge or wall thickness).
- Flow and velocity at the outfall of the pipe.
- Flow capacity of the pipe (Qpipe).
- Length, material, and diameter of all storm drains.
- Property lines, right-of-way limits, street names and widths, finished grade.
- Conflicting underground utilities.
- Drawing numbers for related easements and existing structures.
- Delineation of the drainage basin for the storm drain that includes area calculation.
The procedure for storm drain design proceeds as follows:
Step 1: Size storm drain system on a preliminary basis assuming uniform, steady flow conditions for the peak design discharge.
Step 2: Check the initial pipe sizes using the energy equation, accounting for all head losses.
Step 3: Adjust the pipe size and vertical alignment as necessary to provide minimum HGL freeboard.
COLD CLIMATE HYDROLOGY
The average annual snowfall for our proposed location is approximately 22.1 inches. During the winter season, the melting of snow and the refreezing of the snowmelt can cause damage to drainage infrastructure such as clogging of inlets, pipe damage and leakage, and freezing of sewers. In addition, during the spring, accumulated snow begins its melting process over a period of weeks (typically 2-6 weeks), which results in an increase in snowmelt runoff. It is important to consider these increased peak flows into your calculations and “cold climate” size appropriately by including the base flow for the area that is being considered for development.
COLD CLIMATE ADJUSTMENTS
In order to prevent drainage infrastructure damage, please follow some of the cold climate adjustments given below:
- Avoid submerging inlet pipes into permanent areas of water to prevent pipe ice blockages that could possibly damage pipes or cause upstream flooding.
- Slope inlet pipes to have a minimum slope of 1% to induce flow and prevent standing water that could freeze and cause inlet clogging or upstream flooding.
- Place underdrains and outlet pipes a minimum of 1 feet below the frost line, and increase the pipe size diameter by at least one pipe size.
- The minimum diameter of a perforated pipe shall be no less than six inches and the minimum opening diameter must be one-half inch.
- Align and angle trash racks to prevent ice from forming.
WATER HARVESTING FOR RURAL ROADS
Rural roads are defined as “low volume roads” in rural areas that are made up of materials that range from native soil and gravel to asphalt and even concrete. They are typically found in forest, ranch, and rangeland areas that serve as residential, recreational, maintenance, emergency, and resource management purposes. Rural roads are believed to be cheaper than traditional roads because they come with lower costs and maintenance, however, this is not entirely true. If not properly managed and/or designed, it can lead to sediment transport to watersheds, cause erosion problems, harm the watershed, rivers, creeks, and associated habitats, which come with expensive costs to remedy. To prevent these issues from occurring, it is important to carefully plan and design the grading, drainage, and erosion control plans for the road. Along with this, depending on the city and county requirements, resources such as rainwater can be captured, stored, and reused to control flooding, reduce pollutant and sediment transport, and save on water usage from public water sources.
Rural roads can provide tools for harvesting water if properly managed and designed. Various techniques should be utilized in order to keep these roads from deteriorating and losing their efficiency though. First and foremost, assessments of the site must be made to understand the current road conditions and their future maintenance requirements. In addition, the history, legal status and purpose of the roadways must be analyzed to provide the best course of action.
The topography of the land helps dictate the potential design of slopes, ditches, and drains. Cross slopes for roads should be designed between 5 to 40% and the placement for these roads is best located at the slope’s toe. A site with deep soils provides the best opportunities for low maintenance and low-cost production.
Soil types are an essential factor to consider when constructing a water harvesting rural road. For example, a very clayey/silty soil will not drain well and thus may potentially create a wetland effect during a heavy rainstorm. Due to reduced infiltration of rainwater into the ground, water will begin to collect on the surface and flow across the area. This can lead to issues such as flooding, sediment transport and pollution, and erosion.
On the other hand, using coarse-grained particles ensures drainage. Low-standard roads that are permeable, have adequate amounts of traction, and will resist erosion are composed of textured soils ranging from medium to coarse sized particles. These characteristic traits make medium to coarse soils crucial to maintaining road drainage efficiency and road life expectancy. One element to medium and coarse soils is fine textured soil. Although the finer particles play a smaller role in these soil types, they are integral for maintaining a smoother road over time. If not preserved or taken care of, the roadway will gradually become more rigid due to the densification of the soil and gravel.
During grading, the soil must retain proper moisture in order to provide the most beneficial results. Hydrology is crucial to evaluate, because road conditions will alter based on water inflow and outflow. All aspects of hydrology should be considered when designing for water harvesting. For instance, drier and lower-quality road conditions are found in soils located downhill of the interception point. On the other hand, accelerated loss of soil and the formation of gullies occurs when drainage features are located downhill of the outflow point.
Because construction of rural roads can result in erosion and the formation of gullies, it is crucial to incorporate rocks or landscape swales at the edges of the road. In doing so, runoff water is collected, but must also be diverted to a rock riprap or level spreader. Utilizing these two tools helps control and reduce the water’s velocity in the immediate area. Culverts may also be used in order to transport runoff water from one side of the road to the other. This feature is needed because it directs water away from barriers. For instance, a barrier is created when installing a road along a hill, thus affecting the natural course of runoff water. This barrier could then leave detrimental impacts on the natural habitats that depend on the runoff sheetflowing across the area.
Similarly, installing roads in a wetland region reduces the flow of water and could gradually dry the terrain. This affects various animals that inhabit the ecosystem, such as amoebas, insects, birds and other animals. Culverts can help minimize or eliminate this damage and the drainage outlets should be designed to return the accumulated runoff water at not only a low volume, but also to a soil surface that is undisturbed. This allows for retention of the soil absorption capacity.
Note: If there are no improvements made to an area, then it is considered to be in its original form and “undisturbed”. If we collect the stormwater runoff and outlet it via a pipe towards a riprap which then slowly flows across the undisturbed area, it generally meets code. An exception would be near a creek or river, in which case there would be an additional 100 feet minimum setback.
Ditches are ways to efficiently manage water runoff. Commonly used ditch types include: borrow, wing, lead out, lead in, and cut off ditches.
- Borrow ditches: Shaped as either a “V” or “U” and are established parallel with the roadways. These not only collect water from road surfaces, but they also collect water from hill slopes.
- Wing ditches: Are also shaped as either a “V” or a “U” but these ditches guide water downslope, leading them away from road ditches. If wing ditches are placed too far apart, sediment will accumulate and plug the ditches; therefore keeping runoff water from being harvested.
- Lead-out ditches: May be used to keep the discharge away from the road sides when the water flows from a rolling dip to the downhill side.
- Lead-in ditches: Gather water from a gully and direct the flow through cross drains.
- Cut-off ditches: Should be minimally used, they collect water from flat valley floors and lead the flow through cross drains.
The image below illustrates these various ditch types in addition to others.
With water flow, more often than not, sediments transport and soils erode. To help lessen these effects, drainage features should be spaced more closely together for roads with steep grades and for sites with fine grained soils. In order to create self-cleaning ditches, both the road surface and the ditch must have a slope either equal to or greater than the contributing origin of sediment.
To further manage runoff and ensure drainage, grade reversals are highly suggested. These should be designed every 200 – 300 feet with grades that range from 4 to 10%. Water will not adequately drain when the grade is less than 2% or greater than 15%. Provided below are cross sections of common roads designs that aid with water harvesting. Additionally, proper drainage for these cross slopes must range from 2 to 4%.
Figure: III-3 Alternative Cross Sections Used To Assure Sufficient Cross Sloping And Drainage
CROSS DRAINS
There are various types of cross drains that can be integrated into project sites. Cross drains that primarily apply are rolling dip, flat land, and piped drains.
- Rolling Dips: Rolling drip drains collect and direct surface runoff away from roadways and ditches. They are best used for roads that have slopes varying from 3 to 15%. Rolling dips should not be incorporated on flat terrain or roadways with speeds exceeding 25 mph though.
- Flat Land Drains: Flat land drains should be applied to roads with 0 to 3% grades; the adjacent hillslope must also be less than 5%. Their most useful conditions are for roadways that are either slightly or moderately incised.
Flat Land Drain Schematic
- Piped Drains: Piped drains, also known as culverts, are preferable for insloped or crowned roads. The minimum diameter for the pipe drains is 18 inches, but a 24 inch diameter is ideal. In addition, to ensure that water is properly discharged, cross slopes for culverts must be larger than 2%. These piped drains become unreliable when scheduled maintenance is not guaranteed, making upkeep essential for these drains.
- The image below demonstrates the maximum spacing of cross drains and provides guides for proper placement of these utilities. If no drainage opportunity arises within the provided spacing, the runoff water should drain at the first chance that is provided.
REMOVAL OF BERMS
Berms prove beneficial only when special circumstances apply. Illustrated in the Road Templates image above, berms keep roadway surface water trapped. Specific cases that should utilize berms involve fragile embankments and leading water around a spring source. Routine removal of berms should be included in roadway maintenance practices to keep surface erosion from increasing.
UPSLOPING
An outsloped road, also seen in the Road Templates image above, is effective when the cross slope profile ranges from 2 to 5%. Roads unable to be entirely outsloped could incorporate short segments with a spacing designed at 200 – 300 foot intervals. These segments are most useful when the fill slope resists erosion. The outsloping of roadways could also be used when road grades reach greater than 15%.
MAINTENANCE
Those planning on utilizing rural roadways must set in place practices in order to preserve or extend the lifespan of the roads. In the long run, this will conserve more runoff water and reduce costs. Management of the roads includes prioritizing treatments that address both water harvesting and road maintenance issues. Annual ditch maintenance programs must be put in place, along with routine check ups. During these check ups, vegetation should not be removed unless it impedes drainage. Furthermore, runoff that has been intercepted during the installation of drainage features needs to be returned to its natural path. It is also crucial to be aware of vehicles passing during wet seasons because rutting could occur and require costly repairs. To upkeep well performing cross sections, it is crucial to know how to treat an eroding and aggrading ditch. For instance, an eroding ditch may be resolved by widening the ditch, installing cross drains or lead-out ditches, and/or adding energy dissipators. An aggrading ditch can be regulated by making the cross drain steeper, removing debris, or installing lead-out ditches. All-in-all, maintenance practices must be researched and well planned in order to have reliable roadways.
When researched and applied properly, construction, maintenance, and road treatments are integral parts of the process in order to provide efficient roadways. During the maintenance (and construction) process, certain equipment is best suited for specific soil types and design features. For example, the most desirable performance for maintaining ditches and installing culverts is achieved with rubber-tired tractors. The removal of berms is effective with motor graders. Small farm tractors aid with light grading or drain cleaning.
FIRE DEPARTMENT ACCESS
DESIGN REQUIREMENTS FOR FIRE DEPARTMENT ACCESS
- Buildings and Facilities – For fire access roads, the required extended length from the exterior wall of a facility must be within 150 ft. However, there are some exceptions:
- The building has an approved sprinkler system based on codes in section 903.3.
- In some cases, several factors such as topography, waterways, and building location may not allow access roads installation. In this situation, another authorized fire protection option must be provided.
- Buildings classified as R-3 or U descriptions can be found here.
- In some circumstances, such as when extreme weather conditions cause some access restriction, when single access roads get congested or terrain is difficult to maneuver through, multiple access roads will be required.
- The minimum width of access roads must be 20 ft and the minimum vertical clearance must be 13 ft and 6 inches.
- For roads with inadequate performance/quality, the fire code official has the authority to demand modifications.
- Roads must have the full capacity to endure the loads of fire apparatus and be drivable in various weather conditions, including difficult situations.
- The code official has the authority to determine the turning radius.
- For access roads with extended length greater than 150 feet, an area where the fire apparatus can turn around will be provided.
- In addition, the fire code official shall also determine the maximum grade along with angles of approach and departure of an access road.
- The location of signs and markings that read “NO PARKING – FIRE LANE” will be determined by the fire code official.
- Traffic calming devices will be prohibited unless approved by the fire code official.
Minimum Specifications From Appendix D in 2018 IFC Manual
Dead-End Fire Apparatus Road Turnaround
WATER CATCHMENT
Water catchment systems are designed to capture and store excess rainwater for future use in various purposes of everyday life. These aspects may include washing cars, irrigation, flushing toilets, etc. Water catchment systems also aid in reducing stormwater runoff. The primary purpose of installing water catchment systems is to ensure a decrease in municipal water use during dry seasons by utilizing water that was captured during a wet season. Overall, water catchment systems effectively treat various regions within the country, notably benefitting sectors such as the west and southwest which reach long periods of time without rainfall.
In various circumstances multiple water catchment systems can be used productively. This however, may result in higher costs and may often require larger water storage areas. For several project sites, focusing on a single aspect such as the patio area will be the optimal option. As the Duplicable City Center and Earthbag Village acquire considerable amounts of land, multiple water catchment systems will be applied.
CALCULATING WATER CATCHMENT
To determine the size of the water catchment system and storage, it is essential to calculate the volume of annual captured rainwater. Three main components used to identify the size of the water catchment system are the catchment area along with the amount of rainfall and runoff. Additionally, determine the minimum amount of runoff water that is necessary for capture. This may be established by acquiring the difference between the pre-development runoff and the post-development runoff. Therefore, the volume of rainwater captured from roofs, patios, etc, can be computed using the following equation:
catchment area(ft2) x rainfall(ft/year) x runoff(gal/ft3)
METHODS OF WATER CATCHMENT
Water catchment systems differ depending on the project requirements.With patio water catchment, the most suitable way to capture rainwater is installing a drain/inlet and by sloping the ground around the drain so that water flows into it. Underneath the storm drain is a catch basin which helps separate debris and contaminants from water. The water will then flow into a pipeline that leads to a designated water storage area. The collection of water from streets and impervious surfaces can often be achieved with porous pavements. These roads are composed of materials containing up to 25% of voids allowing for the water to seep through. Another system uses the water that will be treated through a greywater processing pond and later used for irrigation.
CATCH BASINS
A catch basin is a cylindrical hole in the ground commonly lined by masonry blocks and used to hold stormwater. This system then transfers the water into pipes that ultimately discharge into a lake, river, or etc. The water catchment system separates debris from water and is capable of removing trash. As rainwater will be utilized throughout the project, a filtration system is required. The figure below (from Revel Environmental Manufacturing) illustrates how the system functions:
INSTALLATION OF A CATCH BASIN
The installation of a catch basin requires three main processes of installation, which include planning, excavation, and installation:
PLANNING
The location of the catch basin is determined at the beginning of the process. It is vital to consider where water flows when it hits the ground. Once determined, this information will help establish where catch basins should be located and their demand. Additionally, the piping is designed prior to excavation. The piping system is essential to the project because it can effectively distribute the flow during peak hours with little to no overflow. A project engineer may be contacted to determine adequate sizing of the system.
EXCAVATION
The next step in the process is excavating the designated area. The catch basin should be placed at the lowest point of the patio to ensure that the water drains that point. Pipes and natural systems such as gravity will aid with this process of water collection. Then excavate a hole deep enough to place a gravel base underneath the catch basin.
INSTALLATION
Before installing the catch basin, guarantee that the ground is level and stable for the flow of water into the pipe. The drain pipes should have a slight downslope to prevent standing water, which can cause mold and bacteria in the pipes.
DESIGN OF A CATCH BASIN
For the design and installation, a civil engineer and contractor may work together to further detail the plans. At this time, individuals may work on alternative components of the project on their own. Afterwards, analyze the roof system. Rainwater runoff frequently drains from roof tops and requires that gutters efficiently redirect the water. Due to this, determine which gutters are most suitable for the system and determine if it necessary to customize the gutters if the roof is non-traditional. For instance, the Duplicable City Center has a circular roof, indicating that curved gutters are required. When the circumference of the home is approximately 50 feet and based on how many gutter sections requested, add an additional 4 in. to each section. Other features such as elbows, downspouts, and filters can be ordered as well in order to create a more efficient system. After preparations have been completed, proceed as follows:
- Set the pitch and attach the brackets. The gutter has to slope down at ½ in. for every 10 ft. towards the downspout location to ensure it can drain properly. You can use a level to mark a line along which brackets will be hung. Next, drill the brackets into the roof and ensure they are strong enough to hold the gutter.
- Assemble the gutter and cut the downspout hole. Use sealant and pop rivets to attach 2-3 sections at a time, making sure to overlap the middle seams by 4in. You can perform this step on the ground first to make it easier.When the assembled gutter sections are still on the ground in the previous step, you must select the location where you want to cut the downspout hole.
- Hang the gutter and link the elbows, downspouts, and subsurface drainage pipe; if applicable. Next, you will hang the individual gutter connected sections. For sections that are not connected, do so as instructed above in the “Assemble gutter” section. Where downspout locations are specified, attach an elbow to the gutter and connect it to the downspout. For downspouts that directly connect to a subsurface drainage pipe, utilize a downspout to pipe adapter. In cases where a drainage pipe discharges directly into a catch basin, no adapters or extra work is needed.
POROUS PAVEMENTS
Porous pavements are specialized materials used for roadways and paths to filter rainwater runoff. The water collected would later be used to replenish the groundwater levels. Porous pavements have large void ratios therefore allowing the water to seep through. They are useful for various forms of roadways such as driveways, walkways, patios, streets, etc. When utilizing non permeable pavements, the quantity of runoff water increases, and additional practices must be put in place in order to efficiently filter the water. Unlike other pavement types which leave large accumulation of water, when pavements of larger void spaces are utilized, water can be better reused. Permeable pavements are therefore an advantageous approach to sustainable practices.Three common permeable pavements are porous asphalt, porous concrete, and decomposed granite. Brief summaries of these are provided below, but refer to later sections for detailed descriptions of each pavement type.
POROUS ASPHALT
This pavement type allows for the infiltration and reallocation of water. Flat lots can be constructed with porous asphalt where puddles will rarely form. The air voids of this pavement typically range from 15 to 20%. The inclusion of a stone reservoir will better filter and remove contaminants from the water.
POROUS CONCRETE
Porous concrete is capable of capturing the runoff that contains the highest amount of contaminants. Its service life can reach up to 20 years and properly manages stormwater runoff. Unlike porous asphalt and decomposed granite, the properties of porous concrete are dependent on its water-to-cement ratio.
DECOMPOSED GRANITE
Also referred to as DG, decomposed granite is composed of fine particles of granite. This material may be used as a xeriscape. Lighter colors of decomposed granite are provided, ensuring that light can be reflected and not absorbed. Lastly this material provides a natural appearance to the project site.
GREY WATER PROCESSING POND
The grey water processing pond utilizes UV light, vegetation, filtration, and sedimentation in order to supply water for irrigation. It is primarily purposed to collect water that has already been used by faucets and showers. Systems will be put in place to direct water to the grey water processing pond. Once collected, cleaning methods will begin. UV lighting is essential for this process because it reduces the number of bacteria in the surface water and is a large contributor to this procedure. Aquatic plants are also utilized as a natural component because these plants need minerals and nutrients to grow. For instance, nitrogen is commonly prevalent within the water system but with the use of aquatic plants, this pollutant is removed. Bacteria and phosphorus, found on the surface waters can also be removed through the usage of wetland plants. Filtration may be installed within the pipe system such as the inlets or outlets to prevent pollutants from entering the processing pond. Lastly, sedimentation allows for larger particles to sink to the bottom of the pond. Such systems may include a settling basin or an outlet pond for the sedimentation of the large particles. Overall, processing ponds are low cost and low energy, making them a desirable feature for not only the client, but also for the wildlife habitats.
IRRIGATION SYSTEM
One Community will be working to minimize the need for irrigation. We’ll do this through low or no-water naturescaping, hugelkultur, swale construction, and other water saving approaches. Some areas will still require irrigation though. We discuss here the options for those areas.
IRRIGATION SYSTEM USES
This is a system that is used to provide water to vegetation. In most homes, a simple sprinkler system can be used to water lawns and plants, but there are various options to provide water to other different areas.For areas with light rainfall and vegetation that needs frequent watering, irrigation systems should be implemented. Other alternatives such as using a regular watering hose may be time consuming and ineffective. In addition, when spending hours watering lawns, people waste a large amount of water. On the other hand, if an irrigation system is used, home owners can significantly save more time and money. There are different options for irrigation systems based on several factors such as your budget, the plants in your garden, the size of an area you need to water, etc. Some main types of irrigations systems are listed below:
Sprinkler Irrigation: A sprinkler system is designed to spread water over a certain area essentially replicating a rain storm.
Sprinkler Irrigation Types:
- Rotary Heads: These heads can spread water across a 15-50 ft radius. They can move back and forth in a circular motion. Even though the rotary heads have low flow rate, their spray force is strong enough to prevent clogging of the sprinkler head and to minimize puddling and runoff.
- Spray Heads: The spray heads are usually fixed in place and the water coming out is in an umbrella shape with small droplets. This is an ideal option for small areas with less than 18 ft spacing between two spray heads.
- Bubblers: Bubblers are used to supply water to the roots of plants. Bubblers are similar to a drip system, however, their flow rate is higher.
Drip Irrigation: A micro-irrigation system that provides water directly to your roots without having to water the surface. The system allows water to drip slowly from the pipes to the roots of the plants and it can be installed from above the surface or buried below the surface. Drip irrigation places water directly into the root zone and minimizes evaporation. Since the system delivers water and nutrients directly to the roots at the right time and in the right amounts, each plant gets exactly what it needs to grow optimally. This also helps significantly in saving water, fertilizers, and other crop protection products.
Drip Irrigation Types:
- Porous water house system: Porous water house uses recycled tires to make its water hose with various small holes along its length. For hedges, garden beds, and rows of shrubs, this system is an ideal choice.
- Watermatic drip system: In order to construct this irrigation system, work with a professional. Watermatic drip system significantly aids in water saving by minimizing evaporation and storing the excess water to water the plants.
- Emitter drip systems: This system works best for landscapes with shrubs. First, a hose with punctured holes at 12-15 inch intervals will be needed. Next, it shall be connected to a water hose faucet. You can bury it underground or leave it above ground.
- Micro misting system: Micro misting is ideal for orchards, vineyards, and other plants that need constant watering (24/7). It supplies water to plant roots, refreshes flowers and helps shallow roots stay cool during hot weather.
Surface Irrigation: Surface irrigation uses gravity to provide water to plants.
Surface Irrigation Types:
- Basin Irrigation: For basin irrigation, embankments can be constructed around vegetation in order to avoid water flowing out. This system works by flooding the crops with water and letting the excess amount soak down into the roots.
- Furrow Irrigation: For furrow irrigation, you essentially dig small trenches in between the crops. Similar to basin irrigation, the system works by flooding the trenches and letting excess water soak into the roots.
- Border Irrigation: The farmland will be divided into long and narrow bays, then a flood gate at the top of the bays will flood them with water.
THE ADVANTAGES AND DISADVANTAGES OF IRRIGATION SYSTEMS
- Sprinkler System: Advantageous aspects to the sprinkler system include its implementation for various circumstances and project types. The sprinkler system can be utilized for large plots of land, notably for areas in need of moisture. On the other hand, a detriment to this irrigation is the high installation cost. Although this may increase initial project expenses, the operational costs decrease over time. Lastly, sprinkler systems can result in an uneven distribution of water, caused by ineffective performance in windy locations and erratic spraying.
- Drip System: Beneficial qualities to utilizing the drip system is that it efficiently uses water because it uses small amounts in longer periods of time. This process allows for the water to soak deeply into the soil along with aiding the plants to grow better. Each location in which a plant grows is targeted because the drip system is capable of providing water to each location needed. It in turn reduces the potential for weed growth significantly. The drip system adapts to each garden and attends to the changing needs of the garden. Detriments to the drip system include its frequent maintenance requirements in order for the drip to function efficiently. If these systems are not properly installed with assistance from a professional, then it may not reduce potential drought conditions.
- Surface System: Surface systems provide positive aspects to each project type because not only is it easy to manage, but it is also less expensive than alternative systems. Due to its sturdy qualities, weather conditions do not significantly affect the irrigation. This system also does not require exceptional water quality. Although highly beneficial to projects, the surface irrigation designing processes are challenging. If the system is not designed adequately, then it will be difficult to reach each point evenly. In addition, deep percolation or surface runoff may occur at the tail end of a field, resulting in water loss.
TEMPORARY IRRIGATION SYSTEMS
In areas where rainfall is constant for watering vegetation, a permanent irrigation system may not be required. For this project, the vegetation around the village will only need a temporary irrigation system for the first couple years to supplement inconsistent rainfall. The temporary system options are listed as following:
- Poly tube and emitter: This system is essentially a drip irrigation system. A poly tube with emitters across its hose length needs to be attached to the water source.
- Thirsty earth: Thirsty earth is a sprinkler system which operates based on a set timer, therefore, it helps a lot in conserving water and saving money. Furthermore, thirsty earth can be used on a large scale up to 45,000 sqft. The price is approximately $1,000. Additional information can be obtained from the following link.
- Yard camel: A yard camel sprinkler system is easy to set up and operate. Sprinklers can be set up around the areas requiring water. It works for both large and small areas, with a radius coverage of 85 feet/sprinkler.
STREETSCAPE AND WALKWAY DESIGN
In the following section, we dive into the many different street types (commercial, residential, industrial/mix-used, special) and their defining characteristics. Each street type is defined by its attributing features, purpose, activity, and amenities. Depending on the area, zoning, street type and community preferences, street types can be customized to better suit the needs of the municipality. From there, we move forward into codes, regulation, design principles, common layouts and types of walkways. We lay out the design recommendations, requirements, and considerations for walkway design and discuss the guidelines for integrating streetscape and walkway design together.
STREET TYPES
Design considerations of streets differ based on various conditions. Project sponsors planning design improvements for a street must begin with the identification of street type and attributing design features. The types of uses (i.e. commercial, industrial, mixed-use, and residential) have different runoff values and different code requirements. These design considerations are then integrated by the design engineer.
Listed below are the different street types:
COMMERCIAL
- Downtown Commercial Streets: Downtown commercial streets often have high pedestrian volumes and high levels of activity during the day. Downtown streets should have wide sidewalks, high levels of pedestrian amenities, and detailed design standards because of their characteristically high levels of pedestrian activity. Downtown commercial streets shall comply with the guidelines of Downtown Streetscape Plan which was adopted in 1995. Details can be found in the following.
- Commercial Throughways: Similar to downtown commercial streets, commercial throughways have high levels of pedestrian activity and important transit service. They move a large number of people across town in a variety of travel modes and attract them to shop, eat, and entertain from across the city. Commercial throughways have high volumes of vehicular traffic, and traffic is often fast and continuous. Due to their high levels of daily activity, they should be designed with a comfortable pedestrian realm that provides physical space and significant pedestrian amenities.
- Neighborhood Commercial Streets: Neighborhood commercial streets are designed for continuous daily activities of people. For commercial districts, it is important to implement short-term parking for customers and space for loading facilities. As parking and loading facilities often compete for the same space, it is essential to manage them effectively so that local businesses and the public realm are both satisfied.
RESIDENTIAL
- Downtown Residential Streets: Downtown residential streets often have high residential densities, large buildings, and high volume of through traffic. The streets should be appropriately designed for residential living, with generous sidewalks, furnishings, and plantings. For residential uses, the streets should also include places for people to gather, relax, and create.
- Residential Throughways: Residential throughways often include frequent driveway cuts and have a high volume of through traffic with fast-moving traffic flow. Due to this characteristic, they are often not designed for residential uses since it might be uncomfortable to walk or live along. For streetscape improvements, it is recommended to provide a usable public realm through curb extensions, landscaping, and sidewalk width increases if there is adequate space to buffer residential buildings from vehicular traffic in the street.
- Neighborhood Residential Street: Unlike the previous types of streets which often include fast-moving and heavy traffic, neighborhood residential streets are often quieter streets with low volume and low speed vehicular traffic. Despite having low levels of daily activity, neighborhood residential streets are still important to the social life of residents. Improvements for neighborhood residential streets shall focus on slowing traffic and provide generous amenities. More additional guidelines can be found here.
INDUSTRIAL/MIXED-USE
- Industrial Streets: Industrial streets mainly serve freight and loading functions, with low levels of activity during a day. They typically include loading docks, large driveways to accommodate heavy trucks, and other auto-serving facilities. Industrial streets often have minimal sidewalks and streetscape amenities. Nevertheless, they should also have a safe and comfortable pedestrian realm for workers and others passing through.
- Mixed-use Streets: Mixed-use streets are wide streets with high volumes of fast-moving through traffic. They serve a variety of low-intensity industrial uses, as well as a growing number of residences, shops, and services. Because the streets are mixed-use, their character keeps changing constantly to serve a variety of needs. Streetscape improvements will include public amenities, landscaping, and other pedestrian safety elements.
SPECIAL
- Parkways: Streets that possess planted regions, typically 15 to 20’ wide, are categorized as parkways. The plants and greenery occupy most of the open space within the edges of roadways and/or medians.
- Park Edge Streets: Park edge streets are designed with open spaces on one side of the street and developments such as residential areas on the other side. This pattern persists for several blocks and commonly occupies the edges of spacious city parks. Examples of park edge streets range from the Golden Gate Park to McLaren Park, and even to those with waterfront portions.
- Park Interior: Streets located exclusively within open spaces such as city parks are classified as park interior streets. Guidelines for these streets have not yet been developed by the city.
- Multi-way Boulevards: With the use of medians, boulevards separate through traffic and local access from one another.
- Ceremonial (Civic) Streets: Ceremonial streets allow for the facilitation of major gatherings. They serve as major civic spaces and are well established attractions and/or public spaces. Although limited throughout the city, these ceremonial streets bring uniqueness to the community.
- Alleys: With a width of 40 feet or less and a public right-of-way, alleys provide a secondary network to street service.
- Shared Public Ways: Shared Public ways provide shared usage of streets to multiple means of transportation among vehicles, bicycles, and pedestrians. These streets are designed as a single-surface.
- Paseos (Pedestrian-Only Streets): Paseos often intermittently or even permanently close their paths to motorized vehicles to guarantee safety to pedestrians-only streets.
STREETSCAPE ELEMENTS BY STREET TYPE
Varying streets suggest varying design considerations based on their current conditions. Designing appropriate features requires a project sponsor to identify street types. Each street type maintains a list of standard elements along with case-by-case additions for each street type.
STANDARD ELEMENTS
Standard elements should be included for all street improvement projects on that street type. The chart below shows several standard improvements by street type, with the rows listing various types of street (downtown commercial, commercial throughway, neighborhood commercial, etc.) and the columns showing standard elements (curb ramps, marked crosswalks, ped signals, etc.) that should be included. The green circle designates “Yes”, the yellow circle designates “Maybe”, and the red indicates “No”, meaning the element is not recommended for the specific street classification.
Table 1 Standard Improvements By Street Type
CASE-BY-CASE ADDITIONS
Case-by-case additions as detailed in the name, depend on the case-to-case basis of a street. Various aspects are taken into consideration such as constraints, community preferences, and budget for maintenance.
The chart below shows case-by-case additions by street type, with the rows listing various types of street (downtown commercial, commercial throughway, neighborhood commercial, etc.) and the columns showing additions (high-visibility crosswalk, special crosswalk treatment, mid-block crossing, etc.) that may be recommended. The green circle designates “Yes”, the yellow circle designates “Maybe”, and the red indicates “No”, meaning the addition is not necessary for the specific street classification.
WALKWAYS
PURPOSE OF WALKWAY DESIGN
Sidewalks play an essential role in commutes. Not only do sidewalks enhance connectivity by promoting walking, but they are also perceived as conduits for the access and movement of pedestrians. These aspects of walkways serve the city by socially and economically activating the surrounding public spaces. Sidewalks serve as a gateway to city life. By enhancing accessible and safe sidewalks, the health of the general public and maximization of social capital are strengthened. Therefore, creating a worthwhile investment for cities and their communities.
Below, we discuss in detail the considerations for sidewalk zoning requirements, determining minimum width requirements, layout regulations, aesthetics and practical guidelines/recommendations to consider in order to harmoniously integrate streetscape elements and walkway design.
SIDEWALK WIDTHS
CONSIDERATION FOR SIDEWALK WIDTH DETERMINING
- Street Types: Sidewalk width will be determined based on street types (residential, commercial, industrial, mix-use) and levels of daily activity. The specific minimum and recommended sidewalk widths for various types of street can be found in the table in the following section.
- Adjacent Land Use: High-intensity uses attract a greater number of pedestrians, generally requiring greater sidewalk widths.
- Adjacent Building Form: For building form, taller buildings usually have bigger shadows; larger sidewalks give more separation from the buildings, allowing sunlight to reach sidewalks opposite tall buildings.
- Adjacent Ground Floor Use: Buildings with active and busy ground floor activity often take more space on the sidewalks with merchandise displays and seating. This may put some constraint on the sidewalk width. On the other hand, residential buildings do not usually front directly onto the street. They are often set back to allow a transition from public to private spaces.
- Roadway Characteristics: Pedestrians often prefer sidewalks that are buffered from moving traffic. High volumes of through traffic would require a wider buffer to provide a convenient walking environment. Additional sidewalk width, landscaping, on-street parking, and bicycle lanes can be implemented as buffers.
MINIMUM SIDEWALK WIDTHS
SIDEWALK ZONES
Sidewalks implement pedestrian travel that is accessible to all in active public spaces. Considerable amenities that properly activate the streets are lighting, landscaping, and merchandise displays. When properly organized, these amenities establish a safer mode of travel.
The five sidewalk zones are:
- Frontage Zone: The area transitioning from public sidewalk to space within a building, also viewed to be adjacent to the property line.
- Throughway Zone: The travel zone for pedestrians when walking along the street.
- Furnishing Zone: The region of the sidewalk utilized for landscaping, trees, streetlights, and transit stops.
- Edge Zone: A portion of the sidewalk where individuals exit or enter their vehicles parked by the curb.
- Extension Zone / Enhancement Zone: With components such as bulb-outs with mid-block plazas, the extension zone is the pedestrian space extending into the parking lane.
Specifically, figure below illustrates the five sidewalk zones in section view:
CONSTRAINED SIDEWALKS
Sidewalk zones must ensure that the width of the sidewalk is constrained; this signifies that the sidewalk width remains below the recommended requirements. For sidewalks with a constrained width limiting the recommended dimensions of the zones, the following criteria design of the street should be met:
- Ensure accommodations for the required access for individuals with disabilities. This includes designing access to not only transit stops but also adjacent uses.
- Devise accommodations based on expected pedestrian use.
- Determine buffering necessary to put in place for sidewalks with active areas and the adjacent traffic.
- Enhancing public realms by integrating design elements such as space adjacent to businesses in order to service seating and displays.
STREETSCAPE LAYOUT
GENERAL LAYOUT GUIDELINES
- Wisely Allocated Limited Space: In consideration of various streetscapes, elements must be located based on requirements and constraints implemented for streetscapes which plan to be allocated on the street. Attentiveness to each requirement benefits regions with limited street space. If not adhered to, streetscape elements may potentially create clutter, limit visibility, or obstruct pedestrian travel.
- Strive for “Wholeness”: Placement of streetscape elements must establish an emphasis on “wholeness”, where placement of streetscapes considers the block in its entirety, and not its individual qualities. To ensure overall uniformity throughout the city, considerations of consistent city aesthetics and long term design goals are essential.
- Accommodate Pedestrian Needs: Positioning streetscape elements efficiently enables pedestrians to comfortably travel along the sidewalks as well as facilitating ease of flow for vehicles. In addition, streetscapes should reflect a diversity of amenities to ensure public enjoyment. Inclusion and design of unique places thus increase community involvement.
LAYOUT GUIDELINES BY ELEMENT
INTERSECTION DESIGN
DESIGN PRINCIPLES
A primary design requirement for intersections promotes not only the safety of the pedestrian, but also their comfort. Examples below demonstrate preferable intersections:
- Encouraging individuals to walk through the creation of safe and inviting realms for pedestrians.
- Minimizing distance pedestrians must cross in order to reduce exposure time and potential conflicts.
- Maximizing visibility for pedestrians and simultaneously designing treatment in order to slow vehicles speed.
- Reducing traffic high speeds, therefore providing drivers a larger reaction time along with decreasing severity of collisions.
- Appropriately reflecting street and transportation context.
DESIGN FEATURES
Given below, we describe design features as well as provide corresponding images for the features given below.
- Visible Crosswalks: Visible crosswalks alert drivers that they are approaching a location with pedestrian crossing. Therefore, the crosswalks need to be well-marked and visible so drivers can see them clearly and prepare ahead of time. In several situations, the crossings may also be raised or colored if appropriate.
- Parking Restriction at Corners: The curb will be marked with different colors to indicate each type of parking restriction. For example, if the curb is painted red, no vehicles can park in that specific spot, or when it is painted blue, only disable drivers can park there. In some cases, restricting parking adjacent to corners provides vehicles and pedestrians a better visibility when approaching intersections.
- Crossing Aids: Crossing aids help pedestrians with disabilities to cross the street safely. For example, ADA truncated domes on sloped curb provide detectable warning surfaces to assist and warn visually impaired/blind pedestrians. Other aids such as pedestrian lighting/hearing features for crosswalks can also be implemented if necessary.
- Tight Curb Radii: Tight curb radii for turning vehicles serve different purposes, including shortening crossing distances, slowing during traffic, and providing better visibility for pedestrians.
- Curb Extensions: For zones with high volumes of pedestrians, curb extensions should be installed. They help to provide better visibility for pedestrians, slow turning traffic, and reduce crossing times.
- Median Refuges: If medians are present, median refuges should be considered. Median refuges are spaces within a median that help improve the safety of pedestrian and bicycle crossings. They give pedestrians a space when they are not able to cross the entire street in the signal time allotted.
- Roadway and Pedestrian Lighting: At night, visibility is significantly reduced, making it less safe for both drivers and pedestrians. Roadway and pedestrian lighting should be implemented at intersections to illuminate streets and crosswalks. Street, signage, and pavement reflectors can also be utilized to improve visibility and increase pedestrian and bicycle user safety.
- Streetscape Elements: Streetscape elements can be placed adjacent to intersections to improve the quality of the public realm and enhance public space. These elements can include trees, decorative fencing, benches, trash receptacles, bicycle racks, newspaper stands, public art, banners, etc.
The figure below illustrates different design features in a typical intersection, with labels (from A to H) corresponding to the features listed in the section above:
More information and details of various street types, streetscape elements by street types, sidewalk widths, sidewalk zones, constrained sidewalks, streetscape layouts, and intersection design are available in the section “Design Complete Street” of the following resources:
LANDSCAPING
Landscape design is the practice of altering and adding visible features on residential/commercial property to enhance functionality and aesthetics. This is typically done by modifying the surface with plants, trees, shrubs, flora, and fauna to create an appealing garden that brings life to the area. There are many ways to design a landscape, however, not all plants, trees, flora, and fauna are sustainable options. According to the Leadership in Energy and Environmental Design (LEED), sustainable landscaping is measured and graded by the efficacy of its design and maintenance, rainwater management, equipment used to clean the building exterior and hardscape, and amount of area that contributes to protecting and restoring the environment. Because One Community Global is dedicated to making sustainability a mainstream option, the landscape design surrounding all of our projects will pass LEED certification. Below we go into detail of the minimum requirements that must be met in order to be considered for a LEED certification. These standards can be found in the LEED credit library or by clicking on this link.
To be considered for LEED certification, the first requirement is to register your project and submit your application to the Green Building Certification, Inc (GBCI). GBCI will then review the project and credit points whenever it meets specific design requirements. Depending on the scope, size, and level of LEED certification desired (Certified, Silver, Gold, or Platinum), requirements vary. For a general landscaping LEED certification, the requirements are given below:
Requirements:
- Efficacy of building design and maintenance
- Rainwater management
- Equipment used to clean the building exterior and hardscape
- Protecting and restoring the environment
To meet this requirement one must:
- Preserve and protect from all development and construction activity 40% of the greenfield area on the site (if such areas exist).
- Restore a portion of the site (including the building footprint) identified as previously disturbed and follow vegetation and soil requirements below.
- Plant a minimum of 6 native species of vegetation that are native or adapted to the project’s EPA’s Level III ecoregion. Include a minimum of 2 out of the following categories: tree, shrub, and ground cover. Designate a portion of the habitat area for a pollinator garden consisting of native flowering plants and totaling at least 30 square feet.
There are several plants that are native to our proposed location and could work well for landscaping. For example, Fremont Mahonia (Mahonia Fremontii) is a robust Utah native shrub that blooms in late Spring (May – June). This plant adapts very well to poor soil condition and hot, dry weather; therefore, it does not require frequent irrigation. For maintenance, it only needs minimal pruning to maintain the desirable shape and regular monitoring for diseases. Fremont Mahonia produces spiny leaves that change colors with maturity, starting with burgundy, then slowly turning to green and then blue-green. In late spring to summer, Fremont Mahonia changes to bright yellow before turning to a sour purple fruit that was used as dye.
Curl-leaf mountain mahogany (Cercocarpus ledifolius) is another Utah native plant that grows naturally in mountainous areas from 4,000 – 10,000 feet. This plant blooms in April – May and has a fair degree of variability in form across the region. It is a broadleaf evergreen with long, narrow aromatic leaves and ornamentally attractive fruit. Curl-leaf mountain mahogany can grow up to 12 feet and its inflorescences are 1 to 10 whitish yellow flowers. Each flower has between 10 to 25 stamens. Cercocarpus ledifolius can be used to make digging sticks and other tools. It can be used as a type of medicine for pulmonary disorders including tuberculosis.
Nettleleaf giant hyssop (Agastache urticifolia) is an aromatic perennial herb with square stems that grows naturally from 5,000 to 10,000 feet in foothills to mountainous areas across the Intermountain West. Nettleleaf giant hyssop belongs to the family of mint, and it has oppositely attached leaves and a dense spike of pink to purple flowers up to 3.5 inches long that bloom throughout the summer. With the extreme heat of summer, plants from higher elevation seed sources, approximately above 8,000 feet, can still survive and grow well even with very minimal irrigation.
Firecracker penstemon (Penstemon eatonii) is a bright-red-flowered penstemon that has demonstrated wide adaptability to common garden conditions regardless of seed source or trial site. Plants bloomed in early spring and grew 1 to 3 feet tall. Plants overwintered successfully at both northern sites, but those from a lower-elevation accession in Carbon County exhibited better overall survival in the heavier soils of the northern sites. Plants survived both sun and part shade in the two southern sites. The species occurs throughout the north-central and southern part of the Intermountain West at elevations ranging from 2,700 to 11,000 feet. Most penstemon species do best in well-drained soils. Overwatering causes rank growth that flops under its own weight. Seed source should not be an issue with this species, either for growers or for retailers seeking an appropriate market, as there were no differences among accessions in winter-hardiness.
For more information about these native plants of Utah, please visit the following resource.
ADA REQUIREMENTS
On September 15, 2010, The Department of Justice adopted revised regulations for the Americans with Disabilities Act (ADA) of 1990, updating accessibility standards as the “2010 ADA Standards for Accessible Design”. These regulations apply for newly constructed and altered projects of state and local government agencies, public accommodations, and commercial facilities. They provide minimum requirements for parking lots, ensuring that they are readily accessible and usable by disabled people. In addition, the revised regulations also demand other structural changes to existing facilities to make sure they meet the minimum accessibility requirements.
The Department has assembled a separate publication of the revised guidance that applies to the 2010 Standards. This “Guide to the ADA Standards Chapters 1 – 5“ provides details of required changes, the reasoning behind those changes, and responses to public comments on the subject matter.
All on-site facilities and features are designed in order to be accessible to all individuals. The application of these requirements are implemented in all permanent and temporary buildings. The only sites that are not required to follow ADA designs are sites that encompass construction, scaffolding, materials storage, construction trailers, etc. The code emphasizes that the elements that should primarily be considered when designing projects are accessible entrances, routes, restrooms, and when needed, elements such as parking/storage. With this in mind, the code outlines requirements for numerous sites: hospitals, amusement parks, storage, judicial facilities, detention facilities, etc.
Some elements were not explicitly specified in this report because they do not correlate with our case study. To reference the source code mentioned in this section, or to reference more detailed code concerning components such as walkways, parking, plumbing, signs/symbols, etc., please see the 2010 ADA Standards For Accessible Design and Permanent Pedestrian Facilities ADA Compliance Handbook. These documents include the specifics for pathways, accessible routes, crosswalks, building elements and assembly areas.
KEY ASPECTS OF THE ADA CODE
The main point of the code is ensuring that all areas are both safe and accessible. All ground surfaces must be stable and slip resistant and slopes must not be steeper than a 1:20 ratio of rise to run. Intersections should have proper curbs and ramps and assure changes in pavement are small enough for wheelchairs and to not present a tripping hazard for anyone visually impaired. Sidewalks at intersections or crosswalks must also have Detectable Warning Surfaces (DWS). Door sizes must be large enough for a wheelchair to easily fit through them. We summarize all of these below but please reference your local codes to make sure you have the most comprehensive and accurate information for your design.
STAIRS AND LANDINGS
For stairs and landings, especially those located outdoors that will be subjected to wet conditions, design must guarantee that the pathways will prevent water from accumulating. For any grates that are added to the design of the drainage plan, the spaces must not exceed 1/2 inch. If there are elongated openings for grates, then the long dimension of the grate must be placed perpendicular to the most popular direction of travel.
Furthermore, accessible routes must not have running slopes that are steeper than 1:20. For sidewalks, the running slope must not exceed the general profile grade of the roadway. At least one route must be provided that meets these requirements and connects accessible buildings and/or facilities. An exemption to this is if vehicular transportation is the only form of access between the accessible elements and pedestrian access is not provided as well.
INTERSECTIONS AND SIDEWALKS
Intersections, streets, or highways, where pedestrian walkways are put in place must incorporate curbed ramps along with sloped sectors. Additionally, vertical changes in the pavement shall not exceed 1/4 inch and must be designed with a clear width of 36 inches. Any change in surface that ranges between ¼ inch and 1/2 inch must be beveled, and anything with a vertical change greater than 1/2 inch must be designed with a ramp. This is demonstrated in the image below.
Note: For existing sites that did not originally incorporate ADA compliance elements into the design, they will most likely need to be upgraded to adhere to all requirements described in the code. When alterations are being made to certain areas of these sites and accessible paths are added, the cost can be limited to 20% of the overall expenses of the area. Check with your local authority to confirm these details and if the cost limitation would apply to you.
ADA compliant sidewalks at intersections or crosswalks must have a Detectable Warning Surface (DWS) included. A DWS is the yellow dome raised pattern where the running slope shall not exceed 8.3%. Additionally, the cross slope of the ramp must be designed with a slope less than 2%. The turning space slopes, known as the landing, must also follow the 2% guideline. Ramp widths for this design must clear 48 inches. The images below illustrate these guidelines.
Note: As long as there is an accessible ADA compliant route to all accessible elements, it does not specify where there need to be sidewalks vs paths. The only exception though to not having an accessible walkway between two accessible buildings is if the path is for vehicles only.
DOORS, ELEVATORS, AND MISCELLANEOUS
General building requirements mention the inclusion of door openings designed with a minimum of 32 inches of clear width. Elevators must incorporate signals both visible and audible into the design and the fire alarm systems for buildings and sites must also have visible and audible alarms. If public telephones are integrated into the design, then wheelchair accessible telephones must also be provided. Plumbing, ADA accessible bathrooms and/or special rooms should also include built-in ADA compliant aspects such as counters and benches.
PUBLIC SEATING AREAS
For assembly areas, such as One Community’s Straw Bale Village amphitheater and the Aquapini/Walipini and amphitheaters, companion seats for wheelchair spaces must be incorporated into the design. These seats shall be dispersed for all levels of the arena and include an accessible route that leads towards them. Viewing angles must also be taken into consideration so that the lines of sight for wheelchair spectators provide a view equivalent or better than what is provided to other spectators. The elevation of these seats shall take into accounts the lines of sight when individuals sitting in the rows ahead are standing or sitting. The width of the wheelchair space when entered from the rear is designed to be a minimum of 48 inches deep. When the wheelchair enters from the side, the width must be a minimum depth of 60 inches. Additionally, aisle stairs for these assembly areas do not need to comply with code that can be found in section 504.4 of the 2010 ADA Standards for Accessible Design.
PARKING LOT DESIGN STANDARDS
There are several codes in the newly adopted ADA Standards, which set out the minimum requirements for parking lots in different aspects. For example, code #206 discusses accessible routes for site arrival points, facilities, spaces, and buildings. Code #208.2 refers to the minimum number of required accessible parking spaces depending on the total number of parking spaces provided in a parking facility. In addition, the minimum width of access aisles serving car and van parking spaces will be addressed in section #502.3.1 of the 2010 ADA Standards. Code #502.6 explains more about the implementation of identification signs with the International Symbol of Accessibility. The section below provides more information, these are key points to be aware of from the new ADA Standards for Accessible Design codes, which include details about general design and accessible routes, required amount of accessible parking spaces, aisle access, identification signs, and other additional requirements.
GENERAL DESIGN AND ACCESSIBLE ROUTES
The general design standards for parking facilities require ADA parking spaces to not only ensure the shortest, but also the most accessible route to the building entrance. For structures with more than one pedestrian entrance, parking spaces need to be incorporated in locations that provide the shortest accessible routes. Site arrival points such as accessible loading zones, sidewalks, and public transportation stops must also provide an accessible route to the building entrances. If the route is exclusively vehicular and does not include pedestrian access, then an accessible route is exempt. Additionally, on site, no less than one accessible route must be designed to connect accessible facilities, spaces, and buildings. The Duplicable City Center ensures these accessibility design standards are met.
Specifically, accessible routes will be provided at applicable locations in the community. However, since our project is a walk-in community, the parking lot will be constructed at a distant location from our main structures, and generally people may have to walk long distances before entering the building entrance. This can be difficult for disabled people. As a result, One Community will permit handicaped-vehicle access via the service and delivery roads to the building. After being dropped off, movement impaired people can use ADA accessible routes to enter the main structure. In addition, One Community will use electric golf-cart vehicles for maintenance and these can be utilized to provide aid for people with disabilities as well. They can help to transport movement impaired people to various places around the village.
REQUIRED AMOUNT OF ACCESSIBLE PARKING SPACES
Off-street parking for a site must include a minimum amount of accessible parking spaces. These requirements are primarily based on the total amount of parking provided by the facility. The Duplicable City Center’s off-street parking consists of over 501 spaces. According to section 208.2 of the 2010 ADA Standards for Accessible Design, a parking facility with 501 to 1000 parking spaces must serve 2 percent of its total to accessible spaces. Accordingly, one van accessible parking space is designed for every six accessible allotted spaces. Therefore, the Duplicable City Center provides ten accessible parking spots and one van accessible parking space. For further details on total required accessible parking spaces, reference Table 208.2 below.
Table 208.2 Parking Spaces
AISLE ACCESS
Each parking space for the facility amounts to 216 (18 feet) inches in length. The minimum width for car accessible parking spaces requires 96 inches (8 feet) and for van accessible parking spaces the minimum width requires 132 inches (11 feet). Furthermore, accessibility aisles are designed alongside these accessibility spaces. Aisles must be a minimum of 60 inches for accessibility parking spaces; however, for a van accessible parking space, the aisle is a minimum of 96 inches.
IDENTIFICATION SIGNS
Identification of the accessible parking spaces encompass the International Symbol of Accessibility. Frequently used signs consist of Sign R99C (CA) or Sign R99 (CA) along with Plaque R99B, illustrated below. Similarly, accessible van parking space signs include the identification of “van accessible.” Placed at each parking facility entrance or at a location in close proximity to the stall, is a parking sign that advises solely persons with disabilities to utilize designated spaces. These signs reside at a minimum of 84 inches above the surrounding surface.
ADDITIONAL REQUIREMENTS
Off-street accessible parking requirements call for a bumper located two feet from the curb, preventing the encroachment of vehicles. The design of each stall must also ensure that no persons with disabilities require the need to walk behind a vehicle that is not of their own. Lastly, accessibility aisles slope no more than two percent, detailed in the figure below.
HANDRAIL DESIGN STANDARDS
Americans with Disabilities Act (ADA) handrail regulations and standards contain important details and descriptions regarding the design for handrails. These handrail regulations can be found on section 505 of the ADA 2010 Handbook and are mandatory for the safety and well-being of both non-disabled and disabled individuals.
Below we provide a summary of the standards the following details are from the ADA 2010 standards. They are not listed to be followed in any particular order. We would like to note that occasional modifications for improvements for any type of standards are common practice, and therefore recommend and advise to verify and check that your information is up to date when implementing these design standards. With this in mind, the section below covers standards for handrails detailing key features such as height, clearance, cross sections, extension requirements and various other features.
- Handrails are required on both sides of stairs with a rise greater than 6 inches on stairways. The only exception to this rule applies to assembly areas. Inside an assembly area, handrails will not be required to be installed on both sides, but will be provided on either side of the ramp or within the aisle width.
- For ramps or walking surfaces, handrails are required if the slope is higher than 1:20 (a ratio of height to width), or 5%. In cases where the walking surface or ramp falls below 5%, handrails are not required; however, if a handrail is installed it is not exempt from following the design standards.
- Handrails must be continuous for the full length of each stair flight or ramp run/length. Inside handrails on switchback or dogleg stairs (see reference images located at end of tutorial) and ramps must be continuous between flights or runs.
- The minimum handrail height for adults is 34 inches with a maximum at 38 inches (965 mm) above the ramp surface and stair nosing (corner edge of the stair). For facilities or areas where children are the main users (e.g. elementary schools), a second set of handrails with a maximum height of 28 (710mm) inches is required. If a second set of handrails is installed, the vertical clearance between the two handrails must be a minimum of 9 inches (230 mm) to prevent entrapment.
- The clearance between a handrail gripping surface (filled black circle in image below) and adjacent surface (e.g. adjacent wall) shall be a minimum of 1-1/2 inches (38 mm).
- The handrail gripping surface (filled black circle in image below) must be continuous along its length and will not have any obstructions along its top or sides. The bottom of the handrail gripping surface must also not be obstructed for anymore than 20% of its length. Wherever horizontal projections from the wall to the handrail are provided, the projections must be a minimum of 1-1/2” below the bottom of the handrail gripping surface.
- Cross section details and standards are split between circular and non-circular cross sections:
- Circular sections: For a circular cross section, handrail gripping surfaces must have a minimum outside diameter of 1-1/4 inches (32 mm) and a maximum of 2 inches (51 mm).
- Non-circular sections: For a non-circular section, handrail gripping surfaces must have a minimum perimeter of 4 inches (100 mm) and a maximum of 6-1/4 inches 9(160 mm) with a maximum cross-section dimension of 2-1/4 inches (57 mm).
- All handrail gripping surfaces and adjacent surfaces must be free of sharp or abrasive elements and have rounded edges.
- Handrail must not rotate within their fittings.
- Handrail extensions are handrail gripping surfaces that extend horizontally beyond the stair flight typically for a distance equal to one tread depth. These handrail extensions are required with the following exceptions:
- The continuous handrails are at the inside turn of a switchback or dogleg stair and ramps.
- The ramp is located within an assembly area. Ramp handrails in aisles serving seating and/or permit crossover within aisles.
- In alterations where full handrail extensions can create a hazardous configuration.
- Handrail extensions for ramps must extend horizontally above the landing (level area of floor or platform used in between runs on a ramp or staircase) for a minimum of 12 inches (305 mm) beyond the top and bottom of ramp runs. The extensions must follow into a wall, guard, or the landing surface, or must be continuous to the handrail of an adjacent ramp run.
- Handrail extensions at the top of a stair flight must extend horizontally for a minimum of 12 inches (305 mm) beyond the first riser nosing (top edge/corner of the landing). The extensions must return to a wall, guard, or the landing surface, or must be continuous to the handrail of an adjacent stair flight.
- Handrail extensions at the bottom of a stair flight must extend at the slope of the stair flight for a horizontal distance equal to the minimum of one depth beyond the last riser nosing (edge or corner of the last stair). The extensions must return to a wall, guard, or the landing surface, or must be continuous to the handrail of an adjacent stair flight.
- A minimum of 80 inches must be provided for all vertical clearances. Any clearances less than 80 inches must incorporate guardrails or barriers located 27 inches above the ground; as detailed in image.
Vertical Clearance
REFERENCE IMAGES
Inside handrails on switchback or doglegged stairs:
Dog Legged Staircase – Click for source
STAIRWAY DESIGN
Stairs are structures that connect one vertical elevation to another and are known to be one of the first human structures to have been created. Today, stairs can be seen everywhere: from public parks, to apartments, office buildings, and skyscrapers, as a means to get from one floor to another, or as an emergency escape route during fires, power loss, and natural disasters. Like other infrastructure, stairs are bound by codes and rules that must be followed for the safety and wellbeing of its users. Depending on the type of stairway (circular, straight), its use (i.e. private or public), and number of occupants, different regulations apply. Listed below are the rules that apply and pertain to the development or installation of stairs, stairways, and/or stairwell within Earthbag Village. For our design, we followed the 2019 California Building Code (CBC). Note that the code provided below applies to the state of California. Please refer to your local city, county, state, or country code as they may have different requirements.
For any stairway serving a building:
- A minimum width of 44” is required if the occupant load is more than 50 persons. For buildings less than 50 persons, a minimum width of 36” is required. Private stairways serving less than 10 occupants may have a minimum width of 30”.
- Trim may not project more than 3 ½” into the required width of the stairway. Handrails may project 3 ½” into the required width from each side.
- The rise and run of the stair have standard requirements for practicality and safety purposes. The rise, also known as the height of the stair, must be no less than 4” and no greater than 7 ½”. The run, also known as the depth, cannot be less than 10” as measured horizontally between the vertical planes of the furthermost project of adjacent treads.
- Every landing shall have a minimum width, in the direction of travel, equal to the width of the stairway. This means that if the minimum width of a stairwell for a building with an occupancy of less than 50 persons is 36”, the landing must have a minimum dimension of 36” in the direction of travel for the landing. A landing is an area surface or platform that is located at the top or bottom of the floor.
- For handrail requirements, please refer to the handrails section.
For the design of our stairs within Earthbag Village, there were a few popular options: concrete, stone, metal, and pressure-treated lumber/wood.
- When it comes to price, pressure-treated lumber was a clear winner. They provide a natural, warm look to the area and are a cost effective choice. Unfortunately, exterior wood stairs don’t survive for very long and are susceptible to warping, fatigue, and a loss in durability. They would require maintenance and need replacing every 10 years.
- Stone stairs are a beautiful alternative to pressure-treated lumber and are weather resistant and low maintenance. Unfortunately, they are a textured design and can become a tripping hazard if not properly maintained. They are also a more expensive option, with an average price of $150 per step.
- Metal stairs are more resilient than wood stairs, but come at a steeper price. The average metal staircase costs about $200 per step vs. $100 per tread. Metal stairs are not only aesthetically pleasing, but are designed to withstand heavier loads and are coated to resist corrosion. For example, a staircase made of galvanized steel can last more than 100 years with almost zero maintenance required. The disadvantages include noise, potential improper installation issues, and susceptibility to corrosion if there is exposure to moisture to the metal underneath the corrosion resistant coating.
- Lastly, we have the option of concrete. As you are aware, concrete is known for its durability, strength, and longevity. Once poured, concrete stairs can last 50-75 years and does not require much maintenance. It also provides a smooth walking surface and isn’t noisy. However, concrete stairs are the most expensive option coming at $300 per step. If rebars are needed, the costs can spike up above $400 per step as well.
For our stairs, we have decided to move forward with pressure-treated lumber with crushed stone that is used for our walkways. The pressure-treated lumber will be used for formwork and crushed stone will be used as fill. There are many reasons behind why we have decided to move forward with this option. First, pressure-treated lumber and crushed stone provide a very natural look. To add, they are the most cost-effective option and the surface is permeable. With crushed stone costing about $45 per cubic yard. All stairs within Earthbag Village will be installed using the materials mentioned above. Below a CAD drawing of Earthbag Village is given with the stairs shown at every cluster of living domes and along the pathway around the Tropical Atrium.
BICYCLE DESIGN
A bikeway designates space for bicyclists apart from motor vehicle traffic. Bikeways play an important role in the traffic system, with the primary purpose of improving the safety of bicyclists. This element accommodates both vehicular and bicycle traffic while regulating and guiding road users in an organized system. Bikeway efforts compliment current road systems while simultaneously providing the needs of bicyclists. Interconnected bikeway networks not only improve bicycle access, but can also provide a higher safety standard for all users. The development of well conceived bikeways has a positive effect on bicyclist and motorist behavior. In addition, providing an interconnected network of bikeways along with education and enforcement improves safety and access for bicyclists.
Having more people travel through the means of a bicycle over the conventional car has many more benefits that stretch far beyond just the safety of pedestrians, bicyclists, and motorists. To list a few, it has proven to reduce environmental pollution, improve mental and physical health, and stimulate the local economy. In the Netherlands, a country that has been measured to have one of the highest happiness level indices in the world, reports that the population uses a bicycle for 30% of all travel done; and believe that it is a high contributing factor to the mental and physical well-being of the population. One Community shares this vision of being mindful of the environment by reducing carbon footprint as well as increasing the physical and mental health of its occupants, and therefore, is offering bikeway facilities to encourage and promote bike riding.
The decision to develop bikeways should be made in coordination with the local transportation agencies. As mentioned in the paragraph above, having more bicyclists can help to cut down greenhouse gas emissions and global climate change; reduce air pollutants, noise pollution, congestion; reduce demand to construct more parking lots since asphalt and other chemicals in parking lots release pollutants in the atmosphere. In the following sections, bikeway facilities type, typical dimensions of a bicycle rider (eye level, handlebar height, operating width and envelope), bicycle user type, facility selection, and general bikeway design will be discussed in detail.
BIKEWAY FACILITIES TYPE
- Shared Roadway (No Bikeway Designation): Shared roadway is where bicycles travel without bikeway designations.
- Class I Bikeway (Bike Path): Bike paths are used in corridors where a wide enough right of way exists, permitting these facilities to be established away from any impact of parallel streets. These paths are mostly utilized along rivers, canals, ocean fronts, on school campuses, and as part of planned developments.
- Class II Bikeway (Bike Lane): Along streets with significant bicycle demand, establishment of bike lanes along corridors provide greater security; this can also be designed in sectors with distinct needs for bike lanes. Intended with the delineation for right of way of motorists and bicyclists, bike lanes grant more predictable movements. Additionally, bike lane accommodation to bicyclists through corridors create sufficient room for side-by-side sharing of streets for vehicles, exclusively motorists and bicyclists.
- Class III Bikeway (Bike Route): Bike routes, categorized as shared facilities, serve to;
- Provide continuity to bicycle facilities such as Class II bikeways; or
- Allocate preferential routes though higher demand corridors.
- Class III sidewalks as bikeways are discouraged because bike routes normally share the lane with motor vehicles.
- Class IV Bikeway (Separated Bikeway): Class IV Bikeways, also known as separated bikeways, are designed exclusively for the use of bicycles. This facility type requires a clear separation of the bikeway and vehicular traffic.
BICYCLE RIDER – TYPICAL DIMENSIONS
BICYCLE USER TYPE
- Strong and Fearless – 3%: This group refers to the group of individuals bicycling on roadways, despite traffic conditions. Bicyclists under this category comfortably utilize major streets lanes and ride in a vehicular manner regardless of designated bicycle facilities.
- Enthused and Confident – 16%: Bicyclists categorized under this group, prefer riding in designated facilities, but will accommodate roadway situations. Most cycle comfortably in the bike lanes of major streets.
- Interested but Concerned – 71%: Cautious of sharing roadways with cars, this group is primarily held back by unease, but is inclined to bicycling. These individuals tend to feel uncomfortable cycling on bike lanes of major streets and prefer neighboring low traffic streets or separated pathways.
- No Way, No How – 10%: Individuals falling within this group refrain from bicycling. This occurs because they are either physically unable to cycle or have little to no knowledge of riding a bike. Therefore, this group is the least likely to adopt bicycling.
FACILITY SELECTION
Level of Traffic Stress (LTS) as shown below. The goal of understanding these is to provide a safe and efficient network of bikeways that meet all the necessities of local residents. An LTS specifies facility types by matching them to the key needs of cyclists.
Traffic volumes affect the types of bikeways used on projects. Each design is dependent on the estimated vehicles per day in order to ensure the safety of all bicyclists. Using the levels of traffic stress (LTS) below, local streets such as a bicycle boulevard and a Class III bike route are recommended to have LTS 1. Furthermore, the table above categorizes cyclists into three types of riders. This indicates that for LTS 1, the type of bicyclists that will use the lane will range from those who are strong and fearless to those who are interested but concerned. Keeping this in mind, lanes should be designed so that they are suited for all these classes of individuals cycling.
Collector and major roads using Class II bikeways are not recommended when there are more than 5,000 vehicles per day. Referencing the table above, these would leave bicyclists uninterested and occasionally confident. Therefore, for these two street classes, LTS 1 and 2 are recommended with less than 5,000 vehicles per day. If more than 5,000 vehicles a day, the roadway would be classified as a major road and should use a separated bikeway (Class IV).
Recommended Bikeway Type Based on Traffic Volumes
The chart below presents a LTS that corresponds to a crossing treatment based on traffic volumes and the number of lanes used. Six different crossing treatments are provided in correspondence to very low, low, medium and high traffic volumes. Refer to the LTS chart presented previously for specifications of each level of traffic. Ultimately, these recommendations must be followed in order to provide pedestrians and bicycles safe access to various site locations.
Bicycle Boulevard Crossing Treatment Recommendations
RRFB: “The Rectangular Rapid-Flashing Beacon is a device using LED flashing beacons in combination with pedestrian and bicycle warning signs, to provide a high-visibility strobe-like warning to drivers when pedestrians and bicyclists use a crosswalk”.
GENERAL BIKEWAY DESIGN CRITERIA (DESIGN CONSIDERATIONS)
In the following sections we explain the general bikeway design criteria and design considerations to understand before starting your design:
- Widths and Cross Slopes
- Bikeway Separation from a Pedestrian Walkway
- Clearance to Obstructions
- Signing and Delineation
- Intersections with Highway
- Paving at Crossings
- Bikeway Parallel and Adjacent to Streets and Highways
- Bikeway in the Median of Highway or Roadway
- Bikeway Design Speed
- Stopping Sight Distance
- Length of Crest Vertical Curves
- Lateral Clearance on Horizontal Curves
- Grades
- Pavemenet Structure
- Drainage
- Entry Control for Bikeway
- Lighting
WIDTHS AND CROSS SLOPES
- Traveled Way: For one-way bikeways, the minimum paved width of the travel path must be 5 feet. For two-way bikeways, the paved width shall be at least 8 feet, and when applicable, 10 feet width is preferred. For locations where significant pedestrian traffic and high bicycle volumes are anticipated, the paved width of two-way bike paths should be at least 12 feet.
- Shoulder: The shoulder width should be a minimum of 2 feet. A wide shoulder helps to minimize conflict between bicycles and pedestrians. It is usually designed with the same pavement material of the bike path and is placed adjacent to the bike path. If the shoulder and bikeway are constructed with the identical material, the two sections shall be separated with an edge line.
BIKEWAY SEPARATION FROM A PEDESTRIAN WALKWAY
If there is a pedestrian walkway adjacent to the bike path, pedestrians are expected to use it and the bikeway for bicycles. A separation allowance is permitted between the walkway and bike path in the form of walls, fences, railings, or landscaping, but should not obstruct the line of sight at intersections.
CLEARANCE TO OBSTRUCTIONS
A horizontal clearance from the paved edge of the bikeway to obstructions should be provided. The minimum clearance must be 2 feet; however, a 3-foot clearance is preferable. If the path is continuously paved with a fixed object such as fence or wall, a 4-inch edge line shall be placed 2 feet from the object to reduce the probability of bicyclists hitting it. A vertical clearance to obstruction across the width of the bikeway shall be at least 8 feet, and when practical, a clearance of 10 feet is preferred.
SIGNING AND DELINEATION
For application and placement of signs, see the California MUTCD, Section 9B. For pavement marking guidance, see the California MUTCD, Section 9C.
INTERSECTIONS WITH HIGHWAY
Grade separations are necessary for locations where cross traffic and bicycle traffic is heavy, since they can help to reduce intersection conflicts. For those locations where levels of traffic is not high, signs such as “STOP” or “YIELD” may be adequate.
Bikeway intersections shall have relatively flat grades. Suitable warnings should be presented to permit bicyclists to stop before approaching intersections. All the street signs and warnings shall be discussed in detail with the District Traffic Safety Engineer to reduce any conflicts or errors.
For an arterial street, the crossing should be designed at the pedestrian crossing where vehicles are expected to stop. For a midblock location, street signs such as “STOP” and “YIELD” should be used to designate right of ways. Bikeways’ “STOP” and “YIELD” signs should be shielded when they are visible to approaching motor vehicle traffic. To alert motorists, bike Xing signs can be placed in advance of the crossing. Curbs should be designed with ramps to preserve the utility of the bike path. Curb cuts and ramps should provide a smooth transition between the bicycle paths and the roadway.
PAVING AT CROSSINGS
In order to prevent gravel intrusion on the path, the crossing roadway or driveway, including bike paths or pedestrian walkways, will be paved with a minimum of 15 feet. The pavement structure at the crossing should be adequate to sustain the expected loading at that location.
BIKEWAY PARALLEL AND ADJACENT TO STREETS AND HIGHWAYS
It is recommended to implement a wide separation between bikeways and adjacent highways. The separation from the bicycle path to the parallel street or road should be at least 5 feet plus the standard shoulder width. Bike paths within the clear recovery zone of freeways shall include a physical barrier separation. The separation shall not have sidewalks and curbs. If the speed limit is 45 mph or less, some types of barriers such as fences and dense shrubs can be used as well. It is not recommended to use non-continuous obstacles or those that are low to the ground, such as curbs, dikes, raised traffic bars, etc. as it may result in a bicycle accident.
Bike paths should not be designed immediately adjacent to streets and highways since they can create some serious conflicts at intersections. Careful considerations should be addressed before deciding to provide a bike path adjacent to a street or highway, including factors such as number of conflict points, urban density, speed, and volume.
BIKEWAY IN THE MEDIAN OF HIGHWAY OR ROADWAY
It is not recommended to place a bikeway in the median of a local street, state highway, or freeway since they may require movements contrary to normal rules of the road. There are some issues with such facilities, which can be listed below:
- Motorists may be unprepared when bicyclists make right turns from the median of roadways.
- Devoting separate phases to bicyclist movements to and from a median path at signalized intersections increases intersection delay.
- Conflicts can occur when motorists want to make left turns because they must cross one direction of motor vehicle traffic and two directions of bicycle traffic.
- Where intersections are infrequent, bicyclists may choose to enter or exit bike paths at midblock.
- Visibility between bicyclists on the path and motorists at intersections can be significantly reduced due to the landscape of medians.
BIKEWAY DESIGN SPEED
In order to determine the bikeway design speed, engineers use the same principles and standards as those used to determine highway design speeds. Installation of “speed bumps”, gates, obstacles, posts, fences or other similar features intended to cause bicyclists to slow down are not to be used. Below is the minimum design speeds for different bike paths:
Table 1003.1 Bike Path Design Speeds
HORIZONTAL ALIGNMENT AND SUPERELEVATION
Superelevation is the transverse slope provided to counteract the effect of centrifugal force and reduce the tendency of vehicles to overturn and to skid laterally outwards by raising the pavement outer edge with respect to the inner edge. It is the vertical distance between the heights of inner and outer edges of highway pavement or railroad rails. It is often expressed as a ratio, ranging from 0.04 to 0.12. With superelevation, fast-moving vehicles can safely pass through the curved part of the road with stability. The following figure demonstrates the forces and superelevation for a typical curve portion of a highway or road:
Maximum superelevation is set at 2 percent for all bikeway applications. The minimum radius of curvature can be determined based on different design speeds. For a speed of 20 miles per hour, the minimum radius should be 90 feet. For a design speed of 25 mile per hour and 30 miles per hour, the radius will be 160 feet and 260 feet, respectively. When the radius of curvature exceeds 100 feet for 20 miles per hour, 180 feet for 25 miles per hour, or 320 feet for 30 miles per hour, superelevation is not necessary. In some special cases, if curve radii smaller than those given, supplemental pavement markings and standard curve warning signs shall be implemented. In addition, widening the pavement through the curves can be an option to minimize the negative impact of nonstandard curves.
STOPPING SIGHT DISTANCE
Stopping sight distance is designed to help bicyclists see and prepare for the unexpected. Based on design speed, the minimum stopping sight distance shall be determined. For a design speed of 20 miles per hour, the sight distance should be at least 125 feet. For 25 miles per hour, it is 175 feet and for 30 miles per hour, it is 230 feet. The adequate distance for a bicycle to do a full stop is computed based on the bicycle braking ability, the brake reaction time, the speed of the bicycle, the bicyclist’s perception, and the coefficient of friction between the pavement and the tires. Stopping sight distance is measured from a bicyclist’s eyes, which is approximately 4.5 feet above the ground to an object, which is assumed to be ½-foot high.
LENGTH OF CREST VERTICAL CURVES
LATERAL CLEARANCE ON HORIZONTAL CURVES
Bicyclists have a tendency to ride side by side on bikeways and near the middle of the bikeway if the path is narrow. Therefore, lateral clearances on horizontal curves should be computed based on the sum of the stopping sight distances for bicyclists traveling in opposite directions around the curve. A detailed calculation process of minimum lateral clearance on a bicycle path horizontal curve can be found at the following source.
GRADES
It is recommended that the grade rate for bikeways should not exceed 5 percent. Sustained grades should be limited to 2 percent.
PAVEMENT STRUCTURE
The pavement structure and material of a bikeway shall be designed with a similar design process of a highway. There are several important factors that should be taken into consideration. For example, the driving surface needs to be free of vegetation growth, well drained, smooth, and adequate for all types of weather. Skid resistance quality is also a vital factor and needs to be well maintained, especially when the road surface becomes worn under the action of traffic over a long time period.
DRAINAGE
It is recommended to slope the traveled way in one direction to simplify longitudinal drainage design and surface construction. The bikeway shoulder shall slope away from the traveled way in the range of 2 to 5 percent. This helps to minimize ponding and prevent debris and contaminants from flowing onto the bikeway. With a slightly sloping shoulder, surface drainage can slowly flow down and dissipate easily. Nevertheless, when a bikeway is designed on the side of the hill, a drainage ditch may be placed on the uphill side to intercept the hillside drainage. Catch basins can also be added to carry intercepted water. If the bikeway crosses a drainage channel, culverts are necessary in the design.
ENTRY CONTROL FOR BIKEWAY
Fixed objects such as posts and gates located within the bikeway can cause an obstruction to cyclists and reduce their visibility. These obstacles should only be considered when there are no other measures that can be used to stop unauthorized motor vehicle entry. In addition, if the safety and access problems posed to bicyclists, pedestrians, and other users are more serious than the issues caused by unauthorized vehicle entry.
There are several approaches that can be used to prevent unauthorized vehicle entry:
- Post signs to inform vehicle drivers that the entry is a bicycle path and motor vehicle entry is prohibited.
- The path entry needs to be designed/customized so that it does not look like an access path for vehicles, reducing unauthorized access caused by confusion. The path can be divided into two one-way paths prior to the intersection, separated with features not conducive to motor vehicle use. This helps to reduce the amount of vehicles entering the unauthorized location.
- Evaluate if the signing and entry design aids in preventing and reducing unauthorized vehicle entry. If the problems posed by unauthorized entry are more serious than the crash risks and other issues of obstacles, posts and gates may be considered. If obstacle posts or gates are used, they must not force bicyclists to slow down or stop. For those locations where it is necessary to reduce the bicycle speeds, other options should be considered.
- Collapsible bollards or posts should not be used within the paved area of a bikeway, as they present a crash possibility to bicyclists and pedestrians. When vehicles drive across the collapsible bollards, the obstacles can be separated from their hinges, leaving twisted obstructions on the path surface.
LIGHTING
Lighting helps bicyclists to see the bikeway direction, obstacles, and surface condition more clearly. It also makes people aware of any conflicts or obstructions along the road and intersection. At night, lighting for bikeways is recommended at intersections, sag curves, and at locations where physical obstacles are used to deter unauthorized vehicle entry since it helps to improve nighttime security. In addition, daytime lighting should be considered through underpasses or tunnels.
The average horizontal illumination levels will be determined based on the specific location. It ranges from 5 lux to 22 lux, or lumen per square meter. For those locations with severe security problems, higher levels of illumination may be necessary. Light poles should meet the recommended horizontal and vertical clearances. With consideration for pedestrians and bikeways, luminaires and light poles will be placed at an adequate scale. In addition, the District Traffic Electrical Unit can provide more information and guidance on lighting.
Walkway/Bicycle Design Sources:
- Los Angeles County Bikeways.
- For more information on bicycle user type, facility selection, and bicycle boulevard crossing treatment recommendations, please read more in Appendix F of the “Berkeley Bicycle Facility Design Toolbox” provided in the following resource.
- In addition, section 1002.1 of the following link provides more specific information on selection of the type of bikeway facility and section 1003 discusses further general bikeway design criteria (design considerations).
ROAD DESIGN SPECIFICS
Creating a quality road design is imperative to protect and increase the safety of the public and the environment. Making sure the road is designed to code with proper thickness of materials, sufficient loading capacity, drainage, good ride quality, visibility, and traffic considerations affects the everyday quality of life of the people that will use the road as well as those who live within its vicinity. In the following section, we will describe and go over road design specifics, starting with types of roads and design considerations. From there we will dive into more technical explanations of the design of cross-sections, horizontal and vertical alignments, and traffic level of service. All information and requirements concerning these road design specifics can be found in the Utah Roadway Design Manual as well as the Caltrans Highway Design Manual. The following resources from the Department of Transportation of Utah provides general information and details of roadways: Roadway Design. In addition, the following link is the detailed design manual of highways in the state of California.
First of all, it is important to decide what type of road is selected for the project. There are various types of streets, including residential, commercial, collector, major, and rural streets. Determining the street type in advance will make it easier to determine the average daily traffic and follow their design standards and other considerations. For roadway design, it is necessary to take into consideration the major elements of a road, such as design speed, number of road lanes, lane and shoulder width, average daily traffic, maximum/minimum grade, drainage, sight distance, horizontal/vertical alignments, vehicle types, etc. There will be specific design criteria and standards for each element, which must be followed in order to ensure the safety of the project. Level of Service (LOS) is also another factor that needs to be incorporated into roadway design. It determines the congestion level of a road or a highway by utilizing information of design speed, density, traffic volume vs capacity, etc. LOS will rank the road from A to F, with A corresponding to the highest driver comfort and F noting the worst with excessive delays.
TYPES OF ROAD
Before getting to design standards it is important to determine just what kind of road is needed.
- Residential Streets: Generally designed as low average daily traffic (ADT) roads with widths between 20-24 ft. curb to curb. In these areas the road is generally shared with children playing, people walking, etc.
- Commercial Streets: Located in areas that experience high levels of commerce. ADT in this area can vary between high or very low, depending on the time of day.
- Collector Streets: These area streets with low to moderate ADT designed to transfer vehicles from local streets to major streets. Usually with speeds ranging from 25-45 mph.
- Major Streets: Sometimes referred to as arterial roads, these roads have moderate to high ADT flows and speeds ranging from 45-55 mph. It is not uncommon for these roads to be 4 or more lanes.
- Rural Roads: These can be both local roads or collector roads. Both are generally two lane roads with the differences being shoulder width, design speed, ADT, etc. These are usually in forested areas.
DESIGN CONSIDERATIONS
Below we list different design considerations that go into the development of a road:
- Lane and Shoulder Width: Minimum lane width is generally determined by the number of lanes on the road and shoulder width is determined by type of road.
- Number of Lanes: The number of lanes is usually determined by what kind of road you are constructing. In this case a rural two-lane highway is likely the choice.
- Design Speed: Similar to the number of lanes a standard maximum design speed is given based on the road type.
- Design ADT: This is the average number of vehicles that are expected to travel on the road in one direction on any given day.
- Maximum Grade: This is the grade used to prevent water from standing on the road. The grade can be determined using the type of road and terrain.
- Sight Distance: Design speed and type of vertical curve (sag or crest) are the main factors in determining stopping and passing sight distance.
- Drainage: To prevent the runoff from standing on the side of the road a good drainage plan and design is needed.
- Vehicle Types: Roads that have heavy truck usage can affect the design of vertical and horizontal alignments.
- Horizontal Alignment: Two components of horizontal alignment are curve radius and superelevation. It is important when designing to find the best relationship between design speed and curvature.
- Vertical Alignment: Vertical alignments are made up of grades and vertical curves. They affect sight distance and how a truck would approach a vertical curve without having to greatly reduce its speed.
- Superelevation Rate: This is the transverse slope engineers use to negate the effects to centrifugal force and reduce the possibility for the car skidding or turning over. The max elevation for a two lane highway is 12% and 10% for a multi-lane highway.
The Earthbag Village roadways are 20 feet wide to meet minimum fire access requirements and do not experience high levels of vehicular traffic. Due to this reason, the maximum speeds will be 25 miles per hour, a safe speed when pedestrians are present. Vertical alignments will be set at 2% since it is a relatively flat surface. There will be no need for superelevation because vehicle users in the Earthbag Village will not travel in a circular path or curved path subjected to an outward force that makes vehicles overturn and skidding problematic due to centrifugal force. There are various types of vehicles used within the property, including bicycles, cars, trucks, buses, motorcycles, fire trucks in an emergency, etc.
CROSS SECTION DESIGN
This provides a view of how the actual roadway structure will appear. A roadway cross section design depicts a section of the road path where you can see the lane width, shoulder width, number of lanes, grade, drainage, etc.
Geometric Cross Sections for Two-lane Highways (New Construction)
Geometric Cross Sections for Two-lane Highways (New Construction) – Clear recovery zones and labels
HORIZONTAL AND VERTICAL ALIGNMENT
To create a horizontal alignment you must first gather the minimum curve radius and maximum superelevation. Curve radius can be determined by using design speed and a proposed maximum superelevation. The curve radius and design speed can then be used to find a more specific superelevation.
Curve Radius: e + f = 0.067V2/R
e = Superelevation
f = Side friction factor
V = Design Speed
R = Radius
A vertical alignment is created using vertical curves and the grade difference between the two curves. If you have a negative slope approaching a positive slope you will have a sag curve and if it’s the opposite it results in a crest curve. The type of curve significantly affects the sight distance observed by a driver.
From HDM Figure 202.2
From HDM Figure 204.4
LEVEL OF SERVICE (LOS)
The level of service determines how much congestion is on a road or highway. It is determined using factors such as traffic volume vs. capacity, speed, density, etc. After considering the different variables the road is then given a grade from A to F. A is the best grade a road receives, meaning it is free flowing and drivers are comfortable. The worst is obviously an F, because the road has excessive delays and drivers are frustrated.
RURAL ROADS
As mentioned previously, rural collector roads are generally two lane roads. A roadway of 24 feet is suggested, each lane having a designed width of 12 feet. Shoulders and parkways should also be included. As shown below, the Asphalt Concrete (A.C.) shoulder and the parkway must be a width of 10 feet on both sides of the road. Therefore, the overall width of the design is 44 feet, excluding the parkway.
Figure: Plan – Rural Collector Road
Other design aspects must also be considered when incorporating rural roads into project sites. This includes that, for rural collector roads, the average daily traffic (ADT) is assumed at 7,500 vehicles per day with a design speed of 55 mph. Other specifications such as maximum grades based on terrain and the minimum radius for turns are provided in the chart below.
Table 1-16 Rural Collector Road Specifications
A profile view is provided below for the rural collector road. It illustrates the roadway, shoulder, and the parkway. The image also includes the centerline (CL) that divides the two way street. For more information on rural roads, please visit section 1.7 (1.7.1 Rural Local Road, 1.7.2 Rural Collector Road) of the following resource: Rural Roads – Street Design Manual.
Section A-A: Rural Collector Road
ONE COMMUNITY’S PAVEMENT AND WALKWAYS PLAN (CASE STUDY)
We discuss here One Community’s pavement and walkways plan for development Phase I. As part of our goals to open source our complete road and walkways plans, we show both unlimited and limited expense plans. This is so other projects can see the areas where money can be saved and have an idea of the differences in cost for both approaches.
- Duplicable City Center
- Earthbag Village
- Parking Lot Design
- Easement Access to Property
- Low-traffic Roads Within the Property
- Roadway Costs
- Roadway Initial Costs
- Porous Asphalt vs. Conventional Asphalt Costs
- Unlimited Expense Plan
- Maximized Roadways Cost Table
- Minimized Expense Plan
- Minimized Roadways Cost Table
- Walkway Expenses
- Earthbag Village Pathways Cost Table
- Parking Lot Expense Tables
- Recommendations
- Permeable Interlocking Concrete Paver (PICP)
DUPLICABLE CITY CENTER
The pathways of the Duplicable City Center will consist of decomposed granite. Decomposed granite highly benefits the site visually and environmentally, and was chosen as a result of its various advantageous aspects. To review a description of decomposed granite, refer to the Alternative Pavement Options section in the above outline. This material is manageable for installation and upholding maintenance standards. For example, once weathered or eroded, a layer of decomposed granite can be added and compacted to the existing layer for better reinforcement. Its natural appearance allows for aesthetically pleasing transitions from gardens to villas, therefore offering versatile landscaping. Environmentally, the decomposed granite aids in increasing albedo (light reflectivity) due to its various color options. Lighter colors reflect the sunlight, whereas darker pathways and street colors absorb heat, which is then distributed to surrounding areas. This causes an increase in electricity usage for cooling and has scientifically been proven to slowly warm the Earth, the more it is utilized. Another sustainable feature of decomposed granite is its high permeability characteristic, which allows water to move rapidly through rocks and results in high infiltration rates. It is also a Xeriscape, which is a design that reduces or eliminates the need for irrigation and maintenance. With little to no irrigation, this material is used in arid regions (those that do not have plentiful, reliable and accessible supplies of water) and requires less salting for colder temperatures.
Decomposed granite consists of a surface layer of decomposed granite, an optional geotextile fabric layer, an aggregate base course, compacted subgrade, and header board. The decomposed granite layer is made of very small pieces of granite. The sizes can range from a maximum of 1/4″ to a sandy consistency. If a firmer decomposed granite pathway is desired, select the type of decomposed that has stabilizers (which serves as a binder) pre-mixed in. Stabilized decomposed granite is often added on top of another gravel material, tamped down, and left with a thin loose layer on top. This type also has easier installation. Natural decomposed granite is used as a mulch material and can be spread around trees and garden beds like wood mulch. It lasts longer than most other mulch materials and will not attract pests. If a permeable driveway with a more natural look than asphalt is desired, decomposed granite with resin is a good choice.
Header boards are typically 4 inch wide, and they will form the edge of the pathway to contain the decomposed granite. The recommended header boards are pressure-treated redwood, or plastic extruded materials which are weather-proof and will last longer over time.
The geotextile fabric layer is optional. It is a permeable textile material that is buried in the ground. Modern geotextiles are usually made from a synthetic polymer such as polypropylene, polyester, polyethylene and polyamides. It can be woven, non-woven or knitted. Its main functions include increasing soil stability, providing erosion control or aiding in drainage.
For more information, please visit the following websites:
EARTHBAG VILLAGE
For the roadways within the Earthbag Village, porous asphalt has been chosen as the preferred material. Porous asphalt, as mentioned in the Alternative Pavement Options section, is a permeable pavement commonly used for parking lots. Although there are higher tendencies for porous asphalt to be coarse in comparison to other pavements, it still adheres to meet requirements of the Americans with Disabilities Act. In addition, as sustainability requirements are becoming more evident in day-to-day land development, full-depth porous asphalt pavements are now utilized. This pavement can provide substantial cost efficiency in the long term as it is a durable pavement. Potential benefits of porous asphalt, deemed by the Environmental Protection Agency (EPA) state that these pavements not only remove pollutants, but also recharge local aquifers. Thus, due to porous asphalt’s environmentally friendly qualities and cost efficiency, One Community has decided to move forward with this option for the roadways within the Earthbag Village.
Additionally, decomposed granite was chosen for the pathways/walkways within Earthbag Village. This material is more affordable and even more eco-frienly than porous asphalt. It provides beneficial aspects for xeriscaping since it produces little water runoff and, unlike other gravels, when decomposed granite travels (is pushed or washed away), its ability to break down reduces maintenance and upkeep issues. Overall, due to its reduced costs, eco-friendliness, permeability, and aesthetics, decomposed granite is the most suitable material for the design of One Community’s walkways. Therefore, with similar rationale, porous asphalt and decomposed granite were chosen for Earthbag Village.
The top layer is porous concrete, with thickness about 4 inches to 8 inches. Interlocking voids are formed by omitting finer particles that are generally included in their conventional, impervious counterparts. Porous concrete is often poured and cured in place. Concrete materials can also come in a range of colors.
The layer underneath the surface course is the base course, which is constructed of an open-graded ASTM No. 3 or No. 2 stone. The base course acts as a reservoir for the porous pavement system. While these are frequently a single layer, they may also be separate layers with a base course overlying a subbase reservoir. The thickness of the subbase is in the range of 6 inches to 12 inches. This section of the profile will provide the majority of storage for the system.
An additional layer between the base/subbase and subgrade layers can be added, even though it is not required. This layer is geotextile filter fabric. The main function of this course is to improve structural stability of the profile by preventing migration of aggregate into surrounding soil. This layer should extend up the sides of the system to the pavement surface.
The layer underneath the geotextile is subgrade, which is the existing soil layer. This layer must have at least 2 in/h vertical saturated hydraulic conductivity when aggregate is installed. For systems designed to infiltrate into the soil subgrade, the bottom of the system should be at least 2 ft above the seasonal high-water table. This allows the system to recover storage capacity between events by infiltrating into the available pore space within the soil subgrade.
For additional information of porous concrete pavement, please visit the following resource.
The Earthbag Village consists of a 35-foot-wide looped road. For both the roadway’s 1. and the unlimited expense plan, this road is designed as a fire access road. As a fire access road, this pathway consists of porous asphalt and each entrance/exit point of the facility includes a fire access road turnaround. These are incorporated in adherence with the Fire Code in order to allow proper turnaround clearance.
The fire access turnarounds are also the reason the roadway has to be 35’ wide. As originally designed, the Earthbag Village included a narrower road, yet in order to properly integrate the fire access road turnaround design, the road was designed wider. Various access road turnaround plans were attempted to minimize the road width while ensuring proper code compliance. The two major designs that were taken into consideration were the 120’ Hammerhead and the Acceptable Alternative to the 120’ Hammerhead. These Fire Apparatus Access Road Turnaround design elements are illustrated in Figure D103 within the section regarding the Fire Department Access Requirements. The Acceptable Alternative to the 120’ Hammerhead was not chosen as the final design because when placed within Earthbag Village Road, the width of the roadway exceeded 50 feet, as demonstrated in the image below.
In order to efficiently utilize space and materials, the final layout uses the 120’ Hammerhead design, shown below.
As illustrated in this final design, the 120’ Hammerhead lies within the road in order for fire trucks to have sufficient clearance to maneuver to various points around Earthbag Village. All-in-all, the 120’ Hammerhead access road provides safe clearance in accordance with the Fire Code.
PARKING LOT DESIGN
The design of our proposed parking lot will consist of 501 parking spaces, 10 handicap accessible parking spaces, and 1 van accessible parking space. The lot is designed with two rows of parking spaces that flow in one direction. Additionally, the parking spaces are aligned in a diagonal format in the direction of travel and with a lane width of 12 feet.
A fire access path, designed at a width of 20 feet, loops around the right side of the parking lot to adhere to safety protocols and provide visitors with more direct access to parking spots on the other end of the lot. A porous concrete walkway surface runs down the center of the parking lot to give pedestrians access to a safe walking path. Furthermore, bioswales are proposed on the west and east sides of the parking lot for water runoff collection and treatment purposes.
Please view (and click to enlarge) the image to the right for the design of the finalized parking lot. For complete details on sustainable temporary and permanent parking lot design, visit our open source Sustainable Parking Lot Construction Guide page.
EASEMENT ACCESS TO PROPERTY
For One Community, the property is surrounded by national forest land. Therefore, an easement or encroachment permit from a local or state building department must be obtained before development. An easement is a legal right that allows, limits, or gives access to private property for exclusive use such as utility maintenance & repairs and fire access. Whenever you need to access either public or private property or perform work that falls within or affects a neighboring property, an easement or encroachment permit is required. The Forest Service shall determine the terms of such access in a manner that promotes the public interests, protects the natural environment and resources, and follows the agency’s management guidelines. Our guidelines are taken from the United States Department of Agriculture (USDA) and the Los Angeles Department of Water and Power; and these documents can be found using the following links given below:
United States Department of Agriculture Easements for Private Access Information
Los Angeles Department of Water and Power Encroachment Process Information
Since the project location is surrounded by forest land, there will be some restrictions and limitations on the development and construction. Forest roads do not provide year-round and emergency access to residential and commercial zones. For instance, multiple trips of material delivery and heavy construction traffic in wet conditions can severely affect the forest roads. If you plan to use an existing forest road, you may need to prepare for the reconstruction process to properly handle new types of access.
Acquiring an easement is necessary and should be executed before planning a construction schedule. Otherwise, until an easement is approved, you should not access the building site since it can cause some surface disturbance on the forest land.
To get started, first you need to schedule a pre-application meeting with the nearest US Forest Service office to discuss the process of submitting a proposal. A representative of the project can apply for the encroachment process and it does not have to be the owner of the property. Keep in mind that there are several documents and information that you need to prepare in advance:
- Plot Plan or Site Plan: The plan shall be plotted at full scale, showing the existing condition and proposed project. If applicable, it should provide all dimensions for the setbacks and easements.
- Elevations: The elevations that are in or near the easement should be submitted. In addition, they should include height dimensions, deck banisters, roof height, pool equipment, and other construction which comes close to the electrical lines.
- Cross Sections and Parking Layout: If the proposed project demands the construction of a subterranean parking or other underground installations, you will need to submit the elevations, cross sections, and parking layout as well.
- Encroachment Form: You or the representative of your project shall completely fill out an encroachment form. This step can be done in person at the office counter or online by emailing the form in PDF format. It can take anywhere from weeks to months to get a clearance depending on the complexity of the project. There is no cost for this clearance process, unless the owner of the property requests for relocation of the equipment, then an engineering fee is applied.
In addition, the local or state building department may conduct an environmental analysis to examine the impacts of your proposed project on the public lands. This can include whether and how the development can affect ecosystems, local wildlife, protected or endangered species (applies to animals, insects, flora and fauna, etc) that share the habitat. If the project site is located within an Environmentally Sensitive Habitat Area (ESHA), you must receive approval from the local or state building department via data analysis reports from engineers and scientists showing that your proposed development will avoid causing any adverse impacts to the habitat, endangered and/or protected species, and ecosystem. Along with this, the public will have at least one month to give feedback and comment on your project proposal.
Other agencies with jurisdiction of the area may be consulted regarding the impacts of your development as well, depending on the scale and size of land disturbance and development. These agencies can consist of other firms, professionals or experts in the field who are knowledgeable of the area, habitat, local species, native plants, etc. Once an easement is granted, an annual land-use fee will be required for access authorization. Furthermore, easements and permits may also include several maintenance specifications, which may result in some extra annual costs for the property owner.
If you expect the project site to experience heavy snow during cold weather, it is recommended to also include in the road easement application a request for an authorization for the removal of snow. For property adjacent to forest land, removing snow without authorization is a violation of federal regulations and may result in fines.
LOW-TRAFFIC ROADS WITHIN THE PROPERTY
This section reflects upon the roads located outside of Earthbag Village because these roads are composed of a different material. This section also applies to easement access roads, a high-traffic path that leads newcomers to the property parking lot. From there, individuals will be picked up by electric vehicles for a tour and then travel by foot or bike. Additionally, as mentioned previously, heavy delivery trucks and similar vehicles, such as fire trucks, will also use these roads.
Our team researched and compared many different pavement design options and came to the conclusion that porous asphalt would be the ideal choice for the roadways within the Earthbag Village.
Permeable pavement is an alternative to traditional concrete and asphalt in roadway. The permeable pavement design is aesthetically pleasing, promotes infiltration, and reduces runoff. Porous asphalt is a highly permeable material that allows for the infiltration and capture of stormwater. It’s a very good option for a light duty parking facility and a light duty roadway.
The benefits of porous asphalt pavement in comparison with conventional asphalt pavement:
- Porous asphalt pavements have the same, if not possibly twice the amount of design life compared to the conventional asphalt pavement.
- Including installation, the cost of porous asphalt pavement is more expensive than conventional asphalt pavement. However, in terms of maintenance, and water treatment costs, porous asphalt pavement will yield greater monetary benefits than that of conventional asphalt pavement.
- The porous asphalt meets new stormwater regulations: it reduces the total volume of runoff and amount of impervious area, eases the demand for storm sewers, lowers concentration of pollutants, lessens the amount of road closures during heavy rainstorms, and minimizes overall deterioration of the road surface from runoff.
- Since the surface is porous, the pavement won’t suffer from severe ponding issues.
- Porous asphalt pavement reduces the dependency on salt to keep roads clear of ice and snow. Salt has been proven to cause a lot of environmental problems to vegetation and aquatic life. The use of porous asphalt pavements reduces the amount of salt application required during winter storms up to 75%.
CLOGGING PROBLEM
Studies of the long-term surface permeability of porous asphalt and other permeable pavements have found high infiltration rates initially, followed by a decrease that then levels off with time.
SOLUTION:
In order to minimize clogging and promote continued good infiltration rates over time, additional regular maintenance is required. This can be in the form of vacuuming and clearing any vegetation growing through the pores. Clogging issue maintenance requires:
- Inspection of the surface infiltration rates annually during rain events to observe any change in effectiveness of infiltrating stormwater.
- Vacuuming two to four times a year or power-wash, and perhaps more frequently depending on use, to prevent clogging of pores with sediment and fines.
DE-ICING PROBLEM IN WINTER
Salting the road during winter storms prevents slippage and is required for the safety of the drivers in cold climate regions. Even though porous pavements require a lower amount of salt application (by up to 75%) compared to the traditional asphalt pavement, salt is still harmful to the environment, pavement, vehicles, vegetation, and aquatic life. Too much salt can dry out hardscapes, the paws on animals, corrode the metal on the underside of vehicles, damage vegetation, pollute aquatic ecosystems, and create groundwater contamination problems.
SOLUTION:
In order to reduce the use of salt, we have listed a few environmentally friendly ice melt alternatives that are not harmful to the environment:
- Pickle brine: If you pre-wet the pavement with pickle brine, it can keep the snow and ice
from bonding to it, making it possible for the ice to chip away and remove. In winter 2014, pickle brine was used in a large amount in New Jersey to handle a snowstorm and the method was effective despite the unpleasant smell. Brine can work as effectively as traditional rock salt, and it can melt ice at temperatures as low as -6°F (-21°C). Pickle brine is available in many factories and homes with low cost. In addition, it is estimated that brine releases about 14 to 29 percent less chloride into the environment than traditional rock salt does. - Urea: Urea, an organic compound with chemical formula CO(NH2)2, is another alternative to
melt ice. It does not contain chloride, so is less corrosive than rock salt, making it an ideal option for airport pavements (runways, aprons, taxiways, taxiway bridges). Urea can melt ice at a temperature of 15°F (-9.4°C). Urea’s cost is low and it has a very minimal effect on plants and grass. In addition, urea does not require a lot of cleanup compared to rock salt due to its liquid form. - Sugar beet juice: Sugar beet juice is another natural alternative that
can be used to lower the freezing point of water and de-ice roads, sidewalks, and driveways. Sugar beet juice can work effectively to temperatures of -20°F (-28.9°C). Unlike pickle brine which has an unpleasant smell, sugar beet juice is odorless, so you can use it in large amounts without leaving any uncomfortable scent in the area. In addition, this juice is also harmless to humans, plants, cars, animals, fabrics, infrastructure, and water systems. It is also more cost effective compared to rock salt. - Alfalfa meal: Similar to urea, alfalfa meal is a type of organic
fertilizer that can be effectively used as a de-icer. Instead of burning your plants like rock salt does, alfalfa meal contains many nutrients that help to nourish plants and it also does not cause harm to the environment. Due to its characteristic of being dry and grainy, alfalfa meal provides the advantage of additional traction while melting ice and helping vehicles to start, stop, and steer properly on the road. 
Calcium chloride: Calcium chloride (CaCl2) melts ice at temperatures of -25°F (-31.7°C) and it can work 13 times faster than other types of de-icer. Although calcium chloride costs more than some other de-icers, pound for pound it is able to melt twice as much ice. Specifically, it melts up to 8 times as much ice as rock salt does. This 
happens due to its capacity to extract moisture from the surrounding and to cause heat generating reactions (exothermic). It is often applied as a liquid in industrial and highway applications. Calcium chloride is moderately corrosive, even though it is not as bad compared to traditional rock salt, so over-application is not recommended.
Sand, fireplace ash, or coffee grinds cannot be used because it causes clogging of pores. Salt should still be used if absolutely necessary for driver’s safety.
ROADWAY COSTS
There are several factors to consider for roadway initial cost estimates, such as clearing and grubbing; earth excavation; rock excavation; contaminated soil excavation; hazardous waste excavation; major pipe culvert, curb and gutter, median curb, signing and striping, drainage system, traffic signal, sidewalk, and driveway installation. OCG provides two expense plans that go over different scenarios: ideal vs realistic. We compare the two expense plans and have provided a detailed cost analysis table to reflect the differences in the following sections.
The unit cost will be in different units based on each item. For example, for clearing and grubbing culvert, signing and striping, curb and gutter, and sidewalk, the unit cost is given in “per linear foot”. For the drainage system and driveway, the unit cost is given in “per square foot”. And lastly, for excavation, it is given in “per cubic yard” and traffic signals, the price is provided per each unit. The costs per unit can be seen in the images provided below.
ROADWAY INITIAL COSTS
All calculations were also made based on the roadway design of the Total Minimized Expense Plan due to its practicality and higher probability of One Community using that design. Additionally, the Earthbag Village was not considered when formulating these calculations because it has its own cost analysis.
Roadway Initial Costs – Click to open the open source spreadsheet in a new tab
** In the chart above, all items with two asterisks represent elements One Community does not anticipate as part of our design. These items are listed as $0 in our calculations and cost estimates. The costs and resources are still provided here though for those who anticipate these variables and would like to use these charts as a template.
The chart also has an asterisk placed by the drainage system because the analysis requires further clarification. Based on this “Streets, Inlets & Conveyance” document, drainage systems, including inlets and other designs should be incorporated in areas based on their peak flow. It is also highly recommended to place inlets at large intersections in order to prevent water from accumulating.
In the image below, the roadways from the Total Minimized Expense Plan are shown. Eight main intersections are encircled to demonstrate that the most integral pathways that require a drainage system are those in red and categorized as the fire access paths. It is the lengths of these roads which were used to calculate the drainage system cost analysis these design considerations are based on.
Roadways From The Total Minimized Expense Plan
Roadway Maintenance Costs – Click to open the open source spreadsheet in a new tab
* Costs that vary based on other variables. For instance, higher costs are expected for sweeping in areas with colder weather conditions. Additionally, ditch cleaning is dependent on the terrain and things like the type of soil most prominently seen on the site. Removal of a hazardous tree relies on the size of the tree.
** These are items calculated with values from the Unlimited Expense Plan, even though One Community plans on using the Minimized Expense Plan. This was decided because the maintenance provided focuses on asphalt-based repairs, while the Minimized Expense Plan design primarily uses decomposed granite.
Annual maintenance costs are also a consideration that must be considered in the total costs of development for a roadway. The maintenance items of a roadway may include blading, brushing, ditch cleaning, culvert cleaning, tree removal, crack sealing, and pothole repair. With the given unit cost for each item, the total costs for maintenance can be computed. The general formula to calculate the total cost for each item in the chart is:
Total Cost of Each Item = Unit Cost of Each Item (cost per ft, per sq ft, per cubic yard, or per Lump Sum) * The Quantity of Each Item (how many ft, sq ft, cubic yards, or lump sums we need for the project)
Some assumptions were made in the development of our roadway costs calculation. First, the soil that is removed during the “cut” process will be reused for the “fill” process, so all soil will stay on site. In other words, no soil will be imported or exported from the area. In addition, it is assumed that the soil is not susceptible to landslide behavior, and we do not have to treat corrosive soils. There is a very low chance that flooding will occur since it is not mapped within a low point area or near groundwater levels. The soil is not clay or any other types that have the characteristic of poor infiltration capacity, and it has enough bearing capacity to install the roadway without settlement, which is defined as the vertical movement of the ground, generally caused by changes in stresses within the earth. We also make an assumption that there are no trees or heavy vegetation blocking the path and that seismic requirements are minimal or nonexistent. Lastly, the area and development is flat, so there is no need for retaining walls to hold earth back.
POROUS ASPHALT VS. CONVENTIONAL ASPHALT COSTS
The cost of porous asphalt pavement in comparison with conventional asphalt pavement are shown below. This and the following image and analysis of water treatment savings come from “Cost and Benefit Analysis of Permeable Pavements in Water Sustainability.”
Permeable Pavement Costs and Maintenance Comparison – Click to enlarge in a new tab
Water runoff collected from non-permeable pavement also needs to be filtered and treated in some way. Permeable pavement, however, is structured to filter water as it passes through the layers of ground before reaching the groundwater source. The costs of treating water that went through permeable pavement would be $0. The additional benefits of permeable pavement for water treatment is in the amount of money saved by not needing a water treatment center.
Below is data on the installation cost and annual costs of different water treatment practices that could be used if we did not have permeable pavement. We found the costs in terms of the year 2007 and used the present value formula. Here are there different best management plan (BMP) treatment options, their costs in terms of 2007, 2015 and in terms of cubic water treated. The amount of money saved from not treating runoff, represents a large benefit of the installation of permeable pavement.
Best Management Plan (BMP) Water Treatment Options – Click to open in a new tab
UNLIMITED EXPENSE PLAN
The unlimited expense plan is a design that depicts the site roadways for One Community if there were an unrestrained supply of resources. Portrayed by the green hatching, these pathways will be utilized for fire truck, bike, and pedestrian access. These fire access roadways reach within 150 feet of large buildings and facilities, in accordance with the Fire Code. For paths illustrated with the blue hatching, fire access roads will not be incorporated. Instead, bike paths and pedestrian paths are implemented. These roadways reach areas for outdoor facilities and in turn promote usage of sustainable modes of transportation. Lastly the unimproved dirt bike and foot paths are categorized in yellow.
Roadways Unlimited Expense Plan – Click to enlarge
The unlimited expense plan includes a design for the fire access roads composed of either porous asphalt or drain rock. Both provide beneficial sustainable features and result in similar costs. If the drain rock option were to be chosen, two layers would be used, one layer 6” in depth and the other 27”. The base is created from 18″ drainage rock, while 6-8″ of gravel will sit on top. Although the Earthbag Village alsoalso consists of a fire access road that uses porous asphalt. Additionally, the bike lanes would consist of porous asphalt while the walkways of the site, including the Earthbag Village walkways, would consist of decomposed granite. Due to the pedestrian traffic, the decomposed granite pathways are designed with a depth of 3”. In the unlimited expense plan, the parking lot is categorized in green as a roadway that will be utilized for fire truck, bike and pedestrian traffic. While servicing these functions, the parking lot is designed with materials differing from the other roadways. A temporary parking lot of permeable pavement will be constructed and used for several years. When it is time to replace it, it will use asphalt as the final material.
Decomposed granite was chosen for the walkways due to its sustainable properties and cost effectiveness. It provides a xeriscaping pavement design that requires low maintenance and is easily applied. In addition, decomposed granite is highly permeable, allowing water to seep through, reducing runoff water. Similar qualities can be found in porous asphalt, as discussed earlier.
For the safety of individuals, fire access lanes are designed as direct pathways to large buildings/facilities. These provide safe and easy accessibility for the Fire Department. As mentioned previously, fire code requires that each road must reach within 150 feet from the facility. Our design targets the Duplicable City Center and each of the 7 sustainable village models. They also work through the looped campsites and up to the food structures located in the mid-north region of the site.
Note: Class 2 Permeable Base Rock for the surface material is not always recommended because it can dislodge and move around by falling into the grooves of tires. Another concern is if there is runoff flowing into the road, it can clog permeable pavement. This is less of a concern if the area is generally flat, and even less again if the area has proper drainage like ours.
MAXIMIZED ROADWAYS COST TABLE
The table below provides the “Unlimited Resources Roadway Initial Costs” summary for everything described above. It shows the approximate costs for the development of our different roadways, bike paths, and pedestrian walkways if we were to develop them without concern for costs. As shown in the table, the primary materials used to design the pathways of the Maximized Roadways Plan are: decomposed granite, porous asphalt, and ¾” drain rock. Based on the cost analysis and other factors, either porous asphalt or drain rock will be utilized for the fire access roads, therefore both materials are provided in the table below.
Unlimited Resources Roadway Initial Costs – Click to open the source in a new tab
The table below highlights the costs of the roadways for the unlimited plan. The table focuses on the cost of the paths that will be used for vehicular travel; therefore excluding walkways. This allows for One Community to analyze which materials are more desirable and economical for the site’s roadways as there are benefits/detriments to choosing either the porous asphalt or the Class II AB and drain rock. This table also provides a different visual representation of the cost for a better interpretation of the expenses.
Unlimited Plan Roadways Expenses – Click to open the open source spreadsheet in a new tab
Specific roadways were then chosen to explore the unlimited expenses costs that would be associated with our Phase 1 construction rollout. The roadways selected are highlighted in green and yellow below and lead from the entrance of the site to the City Center, Earthbag Village, and Walipini/Aquapinis.
Selected Roadways Unlimited Expense Plan – Click to enlarge
Below you can see the costs associated with each of these areas. Note that the parking lot and Earthbag Village roadways/pathways are not included in this analysis.
Selected Roadways Maximized Cost Table – Click to open the source in a new tab
MINIMIZED EXPENSE PLAN
The minimized expense plan, as the name implies, shows our road and access plan designed to meet code while also saving as much as we can on materials and expenses. Depicted below, it uses green hatchings to represent the electric vehicle access, blue hatchings to demonstrate improved bikeways, and red hatchings to illustrate fire access ways. In addition, dirt paths for unimproved bike and foot paths are shown as yellow.
Roadways Minimized Expense Plan – Click to enlarge
Decomposed granite will be utilized for all pathways on this site plan due to its sustainable features and cost effectiveness. As mentioned previously, fire code requires that each fire truck service road must reach within 150 feet from public facilities. Our design targets the Duplicable City Center, each of the 7 sustainable village models, and the large food structures located in the mid-north region of the site. The fire access road also circles through the Earthbag Village and through the site’s parking lot.
These fire access roads are designed with 6” of decomposed granite, based on standards set forth by the fire code. Similarly, roads utilized for vehicular traffic are suggested to maintain a depth of 5-6”. Therefore, the depth of decomposed granite for electric vehicle access is 6” and improved bikeways are set at 5”. The electric vehicle access reaches through the looped campsites and transitory housing, while dirt paths stretch to zones covering the outdoor class areas and picnic areas. The Earthbag Village fire road is porous asphalt.
The One Community parking lot, although also incorporating a fire access road, will utilize the TRUEGRID® porous system for the first several years. Once the time comes to replace it, the parking lot will be upgraded to asphalt and no further excavations will be necessary.
All roads have been analyzed and deemed safe based on fire code standards.
MINIMIZED ROADWAYS COST TABLE
The table below provides our actual expected roadway initial costs summary for everything described above. It shows the approximate costs for the development of our different roadways, bike paths, and pedestrian walkways with maximum materials and cost savings in mind. Furthermore, the main material used for the minimized roadways cost plan is decomposed granite for all road types.
Minimized Roadways Cost Table – Click to open the open source spreadsheet in a new tab
Highlighted in the table below are the expenses for the roadways of the minimized plan. This table excludes the cost analysis of grading and grubbing, curb and gutter, signing and striping, in addition to the cost of the site walkways. In doing so, One Community can analyze the cost of pathways that will be used for vehicular travel while providing another way to interpret and evaluate the cost.
Minimized Plan Roadways Expenses – Click to open the open source spreadsheet in a new tab
Referencing the image below, highlighted roadways were then selected to be analyzed as part of our Phase 1 construction rollout. These roads lead from the entrance of the site to the City Center, Earthbag Village, and Walipini/Aquapinis. Although the parking lot is highlighted in the image below, it was not included in the cost analysis of these selected roadways because that analysis was completed separately and can be found here. Additionally, the analysis does not include the cost of the roadways/pathways for Earthbag Village itself.
Selected Roadways Minimized Expense Plan – Click to enlarge
The table below reflects the approximate costs of these fire access paths, bike paths and pedestrian paths for the chosen roadways highlighted above.
Minimized Expense Plan Roadway Costs (Selected Roads) – Click to open the open source spreadsheet in a new tab
WALKWAY EXPENSES
The cost analysis below provides the estimated cost for walkways within the site. Unimproved walkways/bikeways were not included in the total cost because they do not use any excess materials. Additionally, since the minimized expense plan does not incorporate a design for pedestrian paths, aside from the unimproved walkways, it is therefore not included in this analysis.
Walkway Expenses – Click to open the open source spreadsheet in a new tab
EARTHBAG VILLAGE PATHWAYS COST TABLE
The analysis provided demonstrates the expected costs for the roadways and pathways of Earthbag Village. Porous Asphalt was used for the fire access road, which is also designed as the main road. On the other hand, decomposed granite was used for all walkways around the dome pods. Please visit here to view information regarding further expenses of Earthbag Village such as the drainage system.
Earthbag Village Pathways Cost Table – Click to open the open source spreadsheet in a new tab
The chart below highlights the roadways expense for Earthbag Village. By removing the cost for cleaning and grubbing, curb and gutter, signing and striping, along with the cost of the walkways, it is easier to view the cost of the roadways that support larger loads such as the fire truck access path.
Earthbag Village Roadways Expenses – Click to open the open source spreadsheet in a new tab
PARKING LOT EXPENSE TABLES
As mentioned previously, two parking lot designs will be applied. Initially, a temporary lot will be utilized for the first few years of the project; once the materials are ready for replacement, the upgraded design of the parking lot will be integrated.
The parking lot will temporarily consist of TRUEGRID material filled with ¾” common gravel. A base rock layer must also be laid and compacted prior to the TRUEGRID installation. These components will not need to be re-excavated when the final design of the parking lot is incorporated. The upgraded parking lot design features asphalt for both the parking spaces and the fire truck access path, which loops around the right side of the lot. A porous concrete walkway will also run down the middle of the parking lot to ensure a safe pedestrian passageway. This parking lot design can be viewed below under the Parking Lot Design Standards section. Additionally, further details on considerations and installation for the temporary and final parking lot can be found here.
Parking Lot Cost Table – Click To Open The Open Source Spreadsheet In a New Bab
Upgraded/final Parking Lot Materials – Click To Open The Open Source Spreadsheet In a New Tab
Landscaping Cost Analysis – Plants Click To Open The Open Source Spreadsheet In a New Tab
Walkways Cost Analysis – Click to View Open Source Spreadsheet in a New Tab
RECOMMENDATIONS
For the major walkway, using Portland cement concrete is recommended. Concrete is one of the most common materials for sidewalk and parkway construction. These walkways have the advantage of being flat, durable, and attractive. Paving in concrete can boast 2 to 4 times the lifespan of asphalt, and concrete also requires less regular maintenance than asphalt. Another great quality about concrete is its customizability. You can shape it to your specific needs and you can change its color.
For minor walkways, decomposed granite is recommended. Decomposed granite is less expensive than Portland cement concrete. It’s highly permeable, relatively easy to install, boasts a long lifespan and low level of required maintenance.
Porous Asphalt (top) Versus Standard Asphalt (bottom) After An Hour and Forty Minutes (right)
PERMEABLE INTERLOCKING CONCRETE PAVER (PICP)
PICP is another option for major walkways. Permeable Interlocking Concrete Paver (PICP) is the most common type of permeable paver. In PICP design the paver is not permeable itself, but the joints are designed to allow water to infiltrate. Permeable pavers consist of solid paving units that are connected using permeable joints. These joints are filled with permeable aggregates that allow water to flow into the open graded subbase below. PICP was estimated at about $10.95 per square foot, including paver, underdrain, and subgrade material.
OPEN SOURCE CONTENT COMING LATER
Once on the property, One Community will open source project-launch blueprint the complete process of installing and maintaining our road and walkway infrastructure. We will do this for everything we think will be helpful for those replicating our system(s) as part of the One Community complete open source self-sufficient teacher/demonstration community, village, and/or city model. Upcoming resources will include:
- Updated complete cost analysis
- Layperson’s guide to purchasing and/or renting all equipment
- Layperson’s guide to working with your county
- Layperson’s guide to installation
- Layperson’s guide to maintenance and upkeep
- Lessons learned during setup and ongoing use/maintenance
- Use this page (click here) if you have a guide/tutorial you’d like to suggest be added here
RESOURCES
General
Project Specific Conditions to Consider
- 2. Article: “Design Input – Equivalent Single Axle Loads”
- 3. Article: “Chapter 610 Pavement Engineering Considerations”
- 4. Article: “Long-Term Pavement Performance (LTPP) Data Analysis Support: National Pooled Fund Study”
Understanding Pavement Structural Layers
Roadways Drainage and Collection
- 6. Article: “Park City StormWater Master Plan”
- 7. Article: “The City of San Diego: Transportation and Storm Water Design Manuals”
Fire Department Access Requirements
- 8. Article: “Fire Service Features”
- 9. Article: “Occupancy Classification / Chapter 3 of the IBC Brief Explanation”
Easement to Access to Property
- 10. Article: “Easements for Private Access Across Public Lands”
- 11. Article: “Department of Water and Power”
Low-Traffic Roads Within the Property
- 12. Article: “Minnesota Stormwater Manual”
- 13. Article: Roadway Improvement Cost Estimates
- 14. Article: Roadway Construction Cost Estimates
Water Catchment
Walkways
- 16. Article: “Downtown Commercial Streets”
- 17. Article: “Design Guidelines by Category”
- 18. Article: “Urban Street Design Guide”
Landscaping
- 19. Article: “LEED Credit Library”
- 20. Article: “Some Good Native Plants for Great Basin Landscapes”
- 21. Article: “Pixabay Photo Resource”
ADA Requirements
- 22. Article: “Code of Ordinances- Chapter 22.112 Parking”
- 23. Article: “2010 ADA Standards for Accessible Design”
- 24. Article: “Permanent Pedestrian Facilities ADA compliance Handbook”
- 25. Article: “Guide to the ADA Standards Chapters 1-5”
Handrail Design Standards and Stairs
Bicycle Design
- 29. Article: “Sign Placement on Shared-Use Paths 2009 Edition”
- 30. Article: “Chapter 9C. Markings 2009 Edition”
- 31. Article: “Chapter 1000 Bicycle Transportation Design”
- 32. Article: “Los Angeles County Bikeways”
- 33. Article: “Berkeley Bicycle Facility Design Toolbox”
Road Design Specifics
- 34. Article: “Roadway Design Manual”
- 35. Article: “Highway Design Manual”
- 36. Article: “Appendix B – Traffic Level of Calculation Methods”
- 37. Article: “Rural Roads”
Porous Asphalt Design
- 38. Article: “Porous Asphalt Pavement Design, Construction and Maintenance”
- 39. Article: “Structural Design of Porous Asphalt Pavements”
- 40. Article: “Porous Asphalt Pavements with Stone Reservoirs”
- 41. Article: “Porous Asphalt Pavements WAPA Technical Bulletin”
Decomposed Granite Paving Design
- 42. Article: “A Crushed Granite Patio or Pathway: Could It be Right For You”
- 43. Article: “How to Install a Decomposed Granite Pathways”
- 44. Article: “Best Small and Large-scale Community Plastic Recycling, Reuse, and Repurposing Options”
- 45. Article: “Decomposed Granite”
Flexible Pavement Design
- 46. Article: “Introduction to Flexible Pavement Design”
- 47. Article: “Flexible Pavement Design Manual”
- 48. Article: “Flexible Pavement Design”
- 49. Article: “California Bearing Ratio and Dynamic Cone Penetrometer”
- 50. Article: “California Bearing Ratio Test”
- 51. Article: “Technical Data – In-situ Testing: California Bearing Ratio”
- 52. Article: “Implementation of the AASHTO Pavement Design Procedures into MULI-PAVE”
- 53. Article: “Pavement Design for Widening Projects”
- 54. Article: “Design Considerations for Flexible Pavement Widening”
- 55. Article: “Treatment Types”
- 56. Article: “Flexible Pavement Maintenance and Repair Techniques”
- 57. Article: “ Pavement – Hot In-Place Recycling”
- 58. Article: “Flexible Pavement Recycling – Caltrans”
- 59. Article: “Thin Maintenance Overlays”
- 60. Article: “Strain Alleviating Membrane Interlayer (SAMI)”
- 61. Article: “SAMI – Stress Absorbing Membrane Interlayer”
- 62. Article: “Full Depth Reclamation Resource Guide”
Pavement Design
- 63. Article: “Rigid versus Flexible Pavement Design”
- 64. Article: “Asphalt or Concrete? The Pros & Cons of Each
- 65. Article: “Composite Pavement Systems: Synthesis of Design and Construction Practices”
- 66. Article: “The Pros and Cons of 6 Driveway Materials”
- 67. Article: “Cost Estimating Guide for Road Construction”
- 68. Article: “Solving Slick Roads and Salty Streams”
- 69. Article: “Minnesota Stormwater Manual
- 70. Article: “Porous Pavement”
- 71. Article: “Minimum Sidewalk Width”
- 72. Article: “Can Pickle Brine Dill-iver Us from Slippery Roads”
- 73. Article: “How to Melt Ice Naturally”
- 74. Article: “Calcium Chloride vs Rock Salt. Which Do You Choose?”
- 75. Article: “Road Salt Alternatives”
Rigid Pavement
- 76. Article: “5 Different Types Of Concrete Joints: How To Make & Repair and What to Fill”
- 77. Article: “Understanding Porous Asphalt”
- 78. Article: “Cost and Benefit Analysis of Permeable Pavements in Water Sustainability”
- 79. Article: “The Benefits of Using Porous Asphalt Pavement in Comparison with Other Forms of Pervious Pavements”
Others
- 80. Definition: “What does walkway mean?”
- 81. Article: “Walkway Materials Guide: Top Ideas + Designs”
- 82. Paper: “Clay Brick – an overview”
- 83. Definition: “Natural stone | Article about natural stone”
- 84. Definition: “CONCRETE”
- 85. Article: “The pros and cons of 6 driveway materials”
- 86. Article: “2020 Concrete Patio Cost | Average Cost To Pour & Install”
- 87. Article: “2020 Stone Walkway Cost | Price of Stone Walkways Per Square Foot, Ideas”
- 88. Article: “How to Seal Pavers on Your Brick Patio”
- 89.Scientific Publication: “Landscape Architecture”
- 90. Article: “Landscaping Costs | How Much | Average Cost”
- 91. Article: “2020 Landscaping Costs | Average Prices List | Per Square Foot & Hour”
- 92. Article: “Cost of Landscaping – Estimates and Prices at Fixr”
- 93. Article: “How to Develop a Budget for Your Landscape Project”
- 94. Article: “2020 Average Cost of Landscaping Maintenance & Prices”
- 95.Article: “Why Every Gardener Should Adopt Naturescaping”
- 96. Article: “How To – Benefits of Native Plants, Native Plant Landscaping and Naturescaping”
- 97. Article: “How to Landscape With Decomposed Granite”
- 98. Article: “How To Build Natural DG Pathways Like A PRO (and how to avoid disaster)”
SUMMARY
One Community’s approach to sustainable roadway and landscaping infrastructure is infrastructure designed to be efficient to construct and with materials, provide high savings in energy and water, be environmentally safe, and economically resourceful. We’ve researched many resources to make our designs replicable, durable, and easy to build and will continue to open source our entire process until a step-by-step tutorial has been provided covering everything a person needs to replicate our designs and efforts. These open source tutorials will be used and evolved as we construct everything on this page and more as part of our 7-sustainable villages construction project.
FREQUENTLY ANSWERED QUESTIONS
Q: What key items should I take away from this tutorial?
One key takeaway is that the implementation of sustainable is essential to all projects. This helps lessen the environmental impacts. By incorporating new designs and providing this information through open source, we can collectively work to provide new advances that can be put into action by individuals, organizations, and corporations.
It is also crucial to take the variables discussed here into account when creating designs and researching sustainable resources. Research further and ensure the advantages and disadvantages of the various technologies, compare all options to guarantee that what is chosen will provide the best results.
Q: How do I apply what I’ve learned in this report?
As a student, engineer, or even as an individual who is interested in developing a more sustainable way of living, it is essential to find new ways to create or include innovation into sustainable infrastructure. Set a goal that each aspect of the proposal embodies protecting the environment, then use the information throughout this report to help guide your small-scale to large-scale projects.
Q: Where should I start my research?
Create an outline on key topics you would like to focus on and determine the primary goals of the research or project. Reference this narrative to help create a basis on what information you would like to continue analyzing. As the research progresses, continue to add further content that reflects what you would like to continue expanding upon. Make sure to refer back to the information you find here as you will find a general format for key information to include.
Q: What are common challenges found when implementing this content?
One substantial challenge was the lack of resources. Some of the most desirable design concepts also require expensive equipment and/or materials. We did our best to work around these obstacles and continue to devise high quality plans. As options were provided, the reasoning behind our decisions have been included throughout the narrative so readers understand and can change the a approach if they disagree or have a better approach. Plans were also devised to demonstrate what materials would have been chosen had there been unlimited resources.
Another challenge was researching the cost analysis. Most designs had multiple materials’ costs, so the individuals researching had to cross reference multiple sources to ensure that the most accurate price point was being used. Some of these values will also rise due to inflation, material availability, etc. So expect fluctuations in these prices.
Lastly, many design variables are predicted to change throughout the project. This will alter other aspects of the project and designs. We will open source share here our evolutions, adaptations and learnings when we actually construct our roadways, walkways, and parking lot(s).
Q: What softwares were used for these designs and are they essential to my own project?
We used AutoCAD and Google Docs and Google Spreadsheets. Civil 3D and Matlab were also used, but not much for this technical report. There are alternatives to these softwares that may be used for your project’s own proposal(s) though. Use what you have available to you and feel comfortable with.
Q: How can I replicate the charts/tables?
Information regarding Roadways and Parking Lot Tables and Charts may be found here: Roadway and Parking Lot Tables and Charts. Each sheet/table provides a small description of what information it entails. Not all charts were applied in the current report, but all have been utilized as our project developed. These sheets may be replicated by creating your own copy of the spreadsheet. Directions for doing this are on the “Intro” tab.
Q: Where can I find additional information about One Community’s projects?
Throughout this narrative, we have linked relevant web pages. Visit our site map for the link to all our open source resources.
Q: I have a resource that I think would be helpful here, how do I share it with you?
If you would like to provide suggestions that will help improve this page, click here.
GLOSSARY
- Albedo: The ratio of light and solar energy reflected by a planet’s surface; high albedo indicates high reflective abilities.
- Atterberg Limits: Refer to the Shrinkage Limit (SL), Plastic Limit (PL), and Liquid Limit (LL) of a soil. These aspects use moisture content to help classify the soil and its plasticity characteristics. These tests help define the soil’s boundaries between solid, semi-solid, plastic, and liquid in addition to helping.
- Bearing Capacity: The amount of pressure or applied loading soil can sustain without failing. Used in geotechnical engineering and the construction industry.
- Best Management Practices: Commonly known as BMPs, Best Management Practices are methods utilized to mitigate surface and groundwater pollution. These can be structural, vegetative or maintenance procedures.
- Bitumen: This is a highly viscous substance used as asphalt; used for not only roadways, but also for roofing.
- Bituminous Stabilization: Strengthens the desired pavement area using additives such as asphalt emulsion, liquid asphalt, or foamed asphalt. This layer must be placed above the subgrade but prior to any new asphalt.
- Chemical Stabilization: Uses additives such as lime, cement, or fly ash in order to strengthen the pavement area it is being placed on. This occurs prior to placing new asphalt.
- Dogleg Stair (switchback stair): A staircase often found in domestic buildings, where a half-landing operates as a midway between successive flights.
- Dowel Bars: Steel bars often placed in concrete or other materials for greater load transfers and as reinforcement.
- Dynamic Loads: Loadings that change in respect to position, direction, and/or time. Often compared against static loads that do not move.
- Catch Basin: A device that allows for water to discharge into the sewer while filtering out large materials.
- Crack Control: The inclusion of reinforcements in order to manage the development of pavement cracks caused by vehicle loads and environmental factors.
- Curing: The process in which concrete maintains sufficient moisture under preferred temperatures.
- Elasticity: A measure of how a material can deform and later return to its original shape. This may include stretching, bending, or compressing.
- Environmentally Induced Degradation: Decay or deterioration caused by environmental factors such as water, wind, rain, etc.
- ESAL Equation. The predicted traffic loading to be furnished by the planning group is the cumulative 18-KIP ESAL axle applications expected on the design lane.
The designer must factor the projected traffic forecast by direction and by lanes (if more than two lanes). The following equation is used to determine the traffic in the design lane for the design period.
- Fatigue Cracking: Excessive traffic loadings cause pavements in distress and failure, leading to the cracking of materials. Also referred to as alligator cracking due to its appearance.
- Fiberglass: A lightweight material resistant to heat that consists of glass and plastic woven together.
- Flexural Strength: Measures the amount of tensile force a material can take without deforming. Also referred to as bending strength or modulus of rupture.
- Geosynthetic Pavement Interlayer: A durable material placed between pavement layers that delay cracking, increase pavement life, and can potentially waterproof the road base.
- Head Losses: Measures the dissipated energy or potential energy lost due to difference of height, pipe friction, valves and more.
- Hydraulic Cement: Cement that hardens and sets at a quick pace after the addition of water. It is often used to stop leaks because of its capability of hardening in water.
- Isolation Joints: A separation placement between adjacent concrete sections.
- Joint saw-cutting: In order for better control on the cracks caused by shrinkage, control joints are created with saw cuts.
- Mechanical Stabilization: Prior to installing or replacing the asphalt, mechanical additives such as reclaimed asphalt pavement, granular materials, or crushed portland cement concrete are laid to enhance the natural capabilities of the soil or layer below.
- Optimum Water/Moisture Content: The content of water in which a soil still maintains after it has been compacted to attain the maximum dry unit weight.
- Pneumatic-Tired Vehicle: A tire commonly used for outdoor free moving vehicles and is composed of rubber and compressed air
- Pressure-treated redwood: Lumber that has been pressure treated, has chemicals penetrated deeply through the surface and body of the wood as a preservative that is intended to resist insects and bacteria.
- Rubberized Pavement Interlayers: Interlayers are primarily used for extending the life of pavement and for its rehabilitation. Due to rubber’s high deformability, it then becomes a stress absorbing membrane.
- Rutting: A permanent depression in the pavement layer caused in flexible pavements by wheel paths. This groove is due to a weak asphalt mixture or thin pavement layers.
- Scarification: This procedure removes flexible pavement surfaces and is part of an in-place road rehabilitation process. It is carried out in order to discard pavement that possesses any irregularities or does not meet standard specifications
- Seal Coats: An overlay composed of a liquid mixture containing emulsified asphalt and takes 2 to 4 hours to cure. It is commonly applied to low volume asphalt based roads. This coat provides protection from raveling, moisture intrusion, and UV damage.
- Skid Resistance: Tires prevented from movement/rotation, create a friction force. Skid resistance is a major characteristic for the categorization of road pavements.
- Subgrade infiltration: Seepage of runoff water that infiltrates the soil/pavement subgrade.
- Subgrade rutting: Depressions of the pavement created by vehicle loadings. This occurs as a result of the binder and aggregate’s ability to move.
- Supplementary cementitious materials (SCMs): Elements that are aggregated to the concrete mixture in order to provide an increase in durability and performance.
- Tensile strength: Measured in force per unit area, tensile strength is the maximum amount of stress applied on a material before it fractures.
- Thermal Cracking: Occurs in various pavement types and affects each differently. For example, in asphalt, low temperatures cause cracks to develop perpendicular to the pavement; while concrete more frequently cracks due to thermal contradictions.
- Traffic Index (TI): Measures the effects of pavement deterioration caused by truck traffic. Necessary for the structural design of roadways.
- Transverse Construction Joint: Joints that are placed in pavements in order to control cracking caused by tensile stresses. Major factors to joint performance are joint spacing, shape, and load transfer.
- Transverse Slope: The difference in elevation between the center of the roadway to the edge of the road over the distance between those points. Also known as a cross slope, this feature provides a drainage gradient for runoff water.
- Xeriscape: A method of landscaping that reduces irrigation and water usage. Especially used in arid and semiarid regions.
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