Volume Reduction of Highway Runoff in Urban Areas: Final Report and NCHRP Report 802 Appendices C through F (2015) / Chapter Skim
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Appendix F Review of Applicability of Permeable Pavement in Urban Highway Environments (White Paper #4) 1 Introduction ....................................................................................................................................
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1 Introduction Why are permeable pavements of specific interest in achieving volume reduction in the urban highway environment? What is the purpose of this white paper?
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• In general, there is still limited information available to help make decisions about use of permeable pavement in the urban highway environment. The purpose of this white paper is to provide an up-to-date analysis of the potential applicability of permeable pavement technologies in the urban highway environment and to provide practical guidance and information to help owners, project managers, and designers navigate the decision process about whether permeable pavements should be considered for a specific project.
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➥ Table o pavements (i.e., permeable asphalt and permeable friction course/open-graded friction course PFC/OGFC) , rigid pavements (i.e., permeable concrete)
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choker course or an asphalt-treated permeable base (ATPB) , an optional filter course (typically included for added water quality treatment)
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with the strength, durability, constructability, and maintenance of the permeable top course, while still making use of storage capacity and infiltration surface area below the road or shoulder. In such a configuration, the designer would need to be conscious of the potential sediment load that would be transported directly into the subbase layers and include provisions for removing sediment in the flows prior to routing flows to the subbase reservoir to avoid premature clogging of the infiltrating surface (below the subbase reservoir)
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control (Thelen, 1978)
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(Briggs et al 2008)
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in Federal Way, WA (Personal Communication, Mark Maurer)
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● Reduce the potential for hydroplaning; ● Reduce the amount of splash and spray; ● Are generally quieter, often providing a 3 to 5 decibel reduction in tire noise when new; ● Improve the wet weather, night visibility of painted pavement markings; ● Filtering and capture of pollutants. Benefits that may be associated with full depth permeable pavements, that are not associated with PFC, include: • High levels of runoff volume reductions can be achieved annually, in many some instances greater than 90 percent of the potential runoff is infiltrated; • Reduction in magnitudes and durations of peak flow rates; • Reduction in temperature of runoff during summer months; • Reduction in the usage of costly drainage infrastructure including catch basins, pipe, ponds, hydraulic control structures, and/or stormwater treatment controls; • Reduction in the use of land area required for stormwater management including limited right of way and adjacent areas; • Improved safety in cold weather climates (reduction in black ice)
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3 Evaluating the Applicability of Permeable Pavement in the Urban Highway Environment While permeable pavements have been used successfully in many applications, including some experience in the urban highway environment, a number of questions remain regarding whether permeable pavements are applicable in a high traffic, high loading, and/or maintenance-constrained environment. This section provides guidance for evaluating these questions for urban highway projects.
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specifics of the project (size, traffic, climate, etc.)
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Design Element Typical Applications in Non-Highway Environment Considerations Specific to the Urban Highway Environment short-circuiting • Required bottom of excavation for soils with poor load bearing capacity or high fines content Subgrade Compaction and Preparation • Subgrade compaction by heavy equipment traffic should be minimized where feasible by construction phasing • Where operation of heavy equipment on subgrade is required, bed bottom should be prepared by scarifying or tilling the subgrade to no less than 20 cm (8 in.) • Avoiding subgrade compaction may be more challenging in roadway construction and/or may be required for strength requirements; a factor of safety in infiltration rates may be needed to account for unavoidable/necessary compaction.
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Design Element Typical Applications in Non-Highway Environment Considerations Specific to the Urban Highway Environment Quality Control • Quality control needs to be documented and implemented during mix production, subbase construction, and materials placement • Application of QC controls in highway environment can leverage the usage of standard QC elements adapted to evaluate infiltration and compaction requirements. Sources: ASCE (2013 in draft)
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would ravel more quickly once the mix oxidized (McGee et al., 2009)
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It is rare that a site would not be suitable for use of permeable pavements solely due to low permeability soils. Permeable pavements typically have a much larger footprint to drainage area ratio than other types of volume reduction approaches, which means that a given storm depth results in a smaller depth of ponding on an infiltrating surface and therefore lower infiltration rates can still infiltrate this runoff in a reasonable time period.
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3.1.6 Geotechnical and Pavement Design Concerns Issue: Does permeable pavement introduce geotechnical and pavement design issues associated with saturated subbase/subgrade that cannot be mitigated? Geotechnical and associated pavement design issues are a key site-specific factor in assessing the feasibility of permeable pavements.
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Careful mix design (especially the selection of the asphalt binder grade, mix production temperatures and the use of additives) is recommended to reduce of the risk of draindown.
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3.1.9 Construction Considerations Issue: Are permeable pavements slower to construct than traditional pavement? Do they pose major issues in the construction process?
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Element Typical Applications in Non-Highway Environment Considerations Specific to the Urban Highway Environment displacement of the mix, and rollers should not be stopped or parked on the freshly placed mat. • Permeable asphalt should not be installed on wet aggregate or wet treated bases or when the ambient air temperature is below 13°C (55°F)
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permeable asphalt and $105/ton for the ATPB (Hodgman 2012)
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parking lot in this study was pavement vacuuming. In this study the permeable asphalt system was found to have the lowest maintenance burden in terms of personnel hours and second lowest annual maintenance costs when compared to the seven other stormwater control measures included in the study.
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Maintenance Activity Summary of Available Guidance Considerations Specific to the Urban Highway Environment and upkeep of permeable pavements. Maintenance Costs • In 2012, the University of New Hampshire (Houle, et.
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equipment (Roseen, et.al., 2013)
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Factors Influencing Applicability Site Assessment and Project Characterization Needs Favorable Conditions Unfavorable/Challenging Conditions Soil and Geotechnical Factors (strength, permeability, and hazards) • Soil texture • Infiltration rates at various degrees of compaction • Assessment of strength under wetted conditions • Granular soils tend to be more favorable • Soils that display limited loss in strength when wet • Soils that maintain some permeability when compacted • Fine grained and plastic soils are more challenging • Soils that exhibit shrink/swell properties • Soils that exhibit substantial loss of strength when wet may require major • Soils that exhibit substantial loss of permeability when compacted (less than approximately 0.01 inches/hour Project Strength and Durability Requirements • What are the pavement system strength and durability requirements for the intended application?
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Factors Influencing Applicability Site Assessment and Project Characterization Needs Favorable Conditions Unfavorable/Challenging Conditions Cold Climate • Freeze-thaw potential • Winter maintenance practices • Agency policies on level of service during cold weather • Temperate climates • If cold climate, then sanding should not be used • If cold climate, Agency would consider permeable pavement as a traction improvement to reduce salt application • Cold climates with sand usage and/or institutional barriers to alternative maintenance practices • Extensive use of studded traction tires Moss Growth Potential • Observation of moss growth on roadways in the project vicinity/region • Exposure of site • Any region where moss growth is not a concern • Sunny sites, with good wintertime exposure and limited potential for tree canopy growth to change exposure conditions • Regions that experience problems with moss growth on shoulders • Sites with poor exposure, particularly with potential for additional shading as trees grow • Roadway segments below grade that maximizes winter shading Type of Highway Segment • Width of shoulder/median • Adjacent slopes • Is back-up drainage critical? • Wider shoulder/median helps provide greater area for permeable shoulders and lowspeed sweeping practices • Relatively mild cross slope helps reduce geotechnical issues • Areas where back-up drainage is not needed • Segments on berms, or in highly constrained sections • Segments on steeper cross slopes • Sag segments or constrained segments where supplemental drainage must be provided as a failsafe for peak flow conveyance Type of Construction • New construction or refinishing / retrofit • Export and import needed to rebuild subbase • Existing drainage/treatment infrastructure already in place • New construction or lane additions where use of permeable pavement can avoid traditional asphalt and conveyance/treatment costs or retrofit construction where subbase is already being rebuilt • Rebuilding subbase would be a major additional cost • Drainage infrastructure is already in place and would not otherwise need to be upgraded • Treatment already provided and would not otherwise need to be upgraded Longitudinal Grade • Review site plans • Flatter segments (less than 1 to 2 percent)
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Factors Influencing Applicability Site Assessment and Project Characterization Needs Favorable Conditions Unfavorable/Challenging Conditions Adjacent Ground Cover • Site plans • Characterization of area draining to permeable pavement • Permeable pavement accepts runoff from only impervious areas • Vehicle tack-on from adjacent areas is limited • Landscaped/pervious areas drain toward permeable pavement (e.g., depressed segment) • Areas with disturbed soils drain toward permeable pavement • Road experiences long-term track-on from adjacent streets/land uses Department Acceptance/ Experience • Evaluate local case studies and research • Review local specifications and design guidance • Local experience and familiarity with permeable pavement design and maintenance • Prior successful installations • Interest in permeable pavement as a pilot project • Negative perceptions about permeable pavement technologies • Lack of experience and/or prior installations Local Contractor Experience and Owner QA/QC Experience • Evaluate past experience/performance with permeable pavement • Visit previous installations and evaluate current performance • Evaluate owner construction QA/QC protocols • Contractor has sufficient past experience (1+ successful installations)
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Factors Influencing Applicability Site Assessment and Project Characterization Needs Favorable Conditions Unfavorable/Challenging Conditions Owner Maintenance Equipment, Capabilities, and Asset Management • Evaluate personnel resources available for pavement maintenance • Evaluate financial resources available for pavement maintenance • Evaluate current asset management and tracking framework • Budget available to purchase a vacuum street sweeper for department use and staff available to operate equipment according to maintenance schedule OR budget available to hire an outside company to conduct regularly scheduled maintenance • Systems in place to track installations and maintenance and ensure that they are not compromised by other road treatments • Budget not available to purchase vacuum street sweeper or to hire an outside company to conduct required maintenance • Systems not in place to track installations and maintenance and/or significant justified concerns that installations would be compromised by other road maintenance DOT and/or Local Contractor Experience with Maintenance • Are maintenance contractors available in the location with experience maintaining permeable pavement? • Can the DOT self preform the maintenance?
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Permeable Pavement Selection and Design Considerations Results of Project-Specific Screening (check the box that applies) Evaluated - not an issue Potential issues must be addressed in design, spec, and construction Prohibitive Owner QA/QC Experience/Protocols Local Supplier Experience Owner Maintenance Equipment, Capabilities, and Asset Management/Tracking DOT and/or Local Contractor Experience with Maintenance 3.3 Permeable Shoulders versus Travel Lane Opportunities Generally, DOT-related practice and research tends to be emphasizing opportunities for permeable shoulders rather than full width permeable pavement across travel lanes.
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4 General Approach for Permeable Pavement Design Integration What is a recommended work flow to help reduce complexity and foster common understanding? Based on the considerations described in Section 3, permeable pavements may be applicable in some cases in the urban highway environment.
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considerations. Section 4.4, below, provides guidance for adapting design features to balance these considerations.
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parameters. In general, permeable materials are not as strong as their traditional counterparts, and a higher degree of saturation in the subgrade material must be considered, which can reduce bearing strength in some types of soil.
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so designs should provide a higher design conservatism (Delatte, 2007)
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one design function results in a depth much greater than needed to serve the other design function. If the base/subbase thickness required for hydrological design is significantly thicker than required for structural capacity, the designer may modify some of the design parameters to make the design more cost effective.
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5 Options for Further Research What are high priority needs and opportunities for further research? Areas of future research can generally be categorized as: • Water quality and quantity performance • System design • Construction methodologies • Quality control testing • Maintenance needs Many studies have been conducted and continue to be conducted on the design and installation of permeable asphalt systems.
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6 Summary Permeable pavements have a number of potentially compelling benefits in the urban highway environment. However, they also have a number of key limitations that may preclude their use in many conditions.
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7 References AASHTO (1993)
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Chai, L., M Kayhanian, B
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Kayhanian, M
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Rasmussen, R.O., R.J. Bernhard, U
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