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:
According to Leadership in Energy and Environmental Design (LEED), sustainable infrastructure is structures and facilities that are highly efficient, provide 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.
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.
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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
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 provided in 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 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 provide 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 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’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.
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:
There are many advantages to asphalt roads compared to rigid roads.
Despite having various advantages, asphalt roads also include several drawbacks.
There are three types of maintenance: preventative, corrective, and emergency.
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.
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.
The most common rigid pavement materials include Portland Cement Concrete (PCC), Rapid Strength Concrete (RSC), and Roller Compacted Concrete (RCC).
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.
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 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.
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 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.
Besides the most common types of pavement listed above, there are other alternatives to consider as well. For instance:
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 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 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 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.
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 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 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 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.
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 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:
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:
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.
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.
The base is composed of selected, processed, and treated aggregate material which is then placed immediately above the subbase.
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.
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.
The inclusion of additional layers depends on either the pavement type, subgrade, or existing soil conditions. These layers may include:
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.
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.
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.
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.
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.
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.
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.
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, 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.
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.
Hydraulic designs are determined after structural requirements have been met. Adjustments should be made if the thickness of the porous concrete is insufficient.
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.
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.
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 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.
Below, we list the materials required to construct a Decomposed Granite (DG) pathway.
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.
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.
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 tmpers
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
In addition there are three methods of HIR:
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.
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.
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.
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.
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.
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.
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.
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
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).
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 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.
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.
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.
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 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:
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:
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:
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 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.
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.
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.
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.
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.
Listed below is an overview of the complete roadway construction process. We discuss the details of the design process in the sections that follow.
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.
Project-specific conditions must be considered before choosing road and walkway pavement choice(s). The various types of considerations are listed and discussed below:
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.
It is important to determine the types of traffic loadings for adequate pavement design. Below is the procedure for traffic loading determination:
In the Highway Design Manual, section 613.3 (Traffic Index Calculation) provides more insight and details into the topic.
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 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 figure below illustrates various climate regions in California and Utah. More information concerning other regions of the US can be found here.
It is important to review the existing pavement type and condition. Some crucial factors are listed below:
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 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:
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:
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.
To get started, items we will need to prepare include:
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:*
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:*
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 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:
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 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.
The design criteria for a storm drain is listed below:**
**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 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:*
Cleanouts must also be located as follows:*
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 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:
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:
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*:
*** 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.
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:
When submitting Storm Drain Plans for design and construction, it must include the following*:
The roadway drainage requirements include the following:
Storm drain plans shall provide a minimum amount of information regarding storm drain design and construction, including all of the following:
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.
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.
In order to prevent drainage infrastructure damage, please follow some of the cold climate adjustments given below:
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. 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%.
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.
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.
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%.
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.
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.
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)
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.
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:
The installation of a catch basin requires three main processes of installation, which include planning, excavation, and installation:
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.
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.
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.
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:
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.
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 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.
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.
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.
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.
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:
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:
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.
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:
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 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.
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.
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.
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:
Specifically, figure below illustrates the five sidewalk zones in section view:
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:
A primary design requirement for intersections promotes not only the safety of the pedestrian, but also their comfort. Examples below demonstrate preferable intersections:
Given below, we describe design features as well as provide corresponding images for the features given below.
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:
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:
To meet this requirement one must:
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.
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.
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.
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, 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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
Inside handrails on switchback or doglegged stairs
Patil, Rahul. “Dog Legged Staircase: Types, Advantages & Disadvantages.” Constructionor.Com, Constructionor, 11 Jan. 2021, constructionor.com/dog-legged-staircase/.
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,
For the design of our stairs within Earthbag Village, there were a few popular options: concrete, stone, metal, and pressure-treated lumber/wood.
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.
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.
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).
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.
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”.
In the following sections we explain the general bikeway design criteria and design considerations to understand before starting your design:
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.
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.
For application and placement of signs, see the California MUTCD, Section 9B. For pavement marking guidance, see the California MUTCD, Section 9C.
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.
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.
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.
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:
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:
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 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.
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.
It is recommended that the grade rate for bikeways should not exceed 5 percent. Sustained grades should be limited to 2 percent.
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.
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.
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:
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:
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.
Before getting to design standards it is important to determine just what kind of road is needed.
Below we list different design considerations that go into the development of a road:
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.
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.
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.
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.
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.
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.
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
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.
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.
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:
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.
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:
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.
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:
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.
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.
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.
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.
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.
** 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.
* 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.
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.”
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The table below reflects the approximate costs of these fire access paths, bike paths and pedestrian paths for the chosen roadways highlighted above.
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.
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.
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.
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.
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.
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.
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:
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.
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.
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.
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.
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).
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.
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.
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.
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.
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