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This report and the accompanying manual summarize the research and resulting guidance developed for achieving surface runoff volume reduction of highway runoff in urban areas. Literature review, synthesis, and focused new analyses were conducted to inform and develop guidance for identifying, evaluating, selecting, and applying volume reduction approaches (VRAs). A stepwise approach was developed and included in the Guidance Manual that guides the user through the evaluation and selection of VRAs. Regulatory and physical considerations were evaluated related to volume reduction in the urban highway environment, and key factors influencing the ability to achieve volume reduction were identified. Recommendations for project-specific site assessment efforts to support volume reduction planning and design were researched and included. Nine primary VRAs were identified that are specifically applicable to the urban highway environment, as well as accompanying site planning and evaluation approaches. A framework for evaluating the applicability, feasibility, and desirability of these VRAs based on site-specific factors was developed. Processes were also developed for prioritizing VRAs and developing conceptual designs. In support of the Guidance Manual, a spreadsheet-based Volume Performance Tool was developed to provide planning level estimates the performance of VRAs, and four white papers on key technical topics were developed. The findings of this research suggest that site-specific conditions are critical in determining the applicability, feasibility, desirability, and effectiveness of VRAs. Additionally, maintaining VRAs is critical for long term effectiveness.

This guidance manual provides practical, research-based evaluation and implementation practices for the reduction of stormwater volumes in urban highway environments. The manual outlines a five-step process for the identification, evaluation, and design of feasible solutions for runoff volume reduction based on site-specific conditions. It is accompanied by a CD-ROM (CRP-CD-162) containing a Volume Performance Tool to assist the user in efficiently estimating the performance of volume reduction approaches and understanding the effects and sensitivity of local climate patterns, design attributes, and site conditions. The manual also includes a set of volume reduction approach fact sheets and a user guide for the Volume Performance Tool. This guidance manual will be useful to DOT managers, project staff and design engineers, permit writers, consultants, and planners.

A wide range of treatment controls (commonly known as “best management practices” or BMPs) have been developed to manage stormwater. Treatment BMPs use various processes to mitigate the impacts of pollutants and altered hydrology; for example, by attenuating the flow or reducing the volume of stormwater or by reducing pollutants with physical, biological, or chemical processes. This report provides information on long-term performance and life-cycle costs for highway-related stormwater BMPs. Information was gathered via literature review, survey of departments of transportation (DOTs), and interviews with practitioners. Information for treatment BMPs was derived from DOT studies and the International BMP Database. The International BMP Database contains performance records for treatment BMP evaluations throughout the United States. The research included conducting a large number of computer simulations using the U.S. EPA’s Stormwater Management Model (SWMM) to quantify runoff volume reduction through the BMP. The report is accompanied by a CD-ROM (CRP-CD-153) containing a BMP evaluation tool in a spreadsheet format as a computational aid that provides average annual performance and whole life costs for treatment BMPs. A guide (Planning Tool Handbook) is provided as Appendix F to quickly orient the user to the basic functions of the tool provided on the CD-ROM. The report will be of interest to state DOT highway design and environmental practitioners.