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Performance Measures, Best Practices and Recommended Design Guidance for Green Streets

Description:

The AAHSTO Green Book, A Policy on Geometric Design of Highways and Streets, states that streets should “serve as a catalyst to environmental improvement” and that landscaping should “mitigate the many nuisances associated with urban traffic.” However, stormwater runoff from streets is a leading contributor to nonpoint source pollution. In the Pacific Northwest, stormwater from streets and urban areas is the biggest single source of pollution for the Puget Sound, and within the Chesapeake Bay watershed stormwater is the fastest growing source of pollution.

To mitigate stormwater runoff from streets and facilitate compliance with the EPA’s NPDES permit program and Combined Sewer Overflow Control Policy agencies from across the country are integrating green stormwater infrastructure into transportation corridors. Cities from every region of the country (Portland, Oregon; San Francisco, California; Chicago, Illinois; Kansas City, Missouri; Austin, Texas; New York, Philadelphia, Pennsylvania) are adopting and implementing so called green streets.

Green streets integrate green stormwater infrastructure (GSI) facilities to manage stormwater runoff within the public right-of-way. These facilities intercept, treat, attenuate, infiltrate or evaporate stormwater runoff. Typical strategies for for use along streets include bioretention cells, permeable pavements and trees. Bioretention cells temporarily pond stormwater runoff and use plants and soil to filter the runoff, either infiltrating or slowing the flow before they enter water bodies or the public sewer system. Permeable pavements reduce the effective imperviousness of a street and allow stormwater to infiltrate into the ground. In addition to the environmental benefits of green streets, these facilities, when appropriately designed, can contribute to an inviting streetscape and pedestrian realm.

Objective:

In the absence of national standards for the design of Green Streets a body of best practices is emerging that considers context sensitive design elements related to street design, character and use, posted speed, traffic volumes and impacts to non-motorized service and vehicular access.

The objective of this research is to:

● Document research and performance of Green Streets and green stormwater infrastructure to treat and control stormwater runoff.

● Document current and emerging best practices, case studies and design guidance for implementing Green Streets.

● Identify design elements of Green Streets and green stormwater facilities (e.g. depths of facilities, edge conditions, offsets, etc) to support safety for all users (pedestrians, bicyclists, drivers) of the transportation corridor.

● Identify ongoing research and initiatives for the planning, design and implementation of Green Streets.

● Identify future research needs and opportunities for Green Streets.

Benefits:

The public right-of-way accounts for more than 20 percent of impervious area in urban areas. As individual agencies develop programs and policies to address stormwater permit requirements they will expend significant resources developing design standards and operational practices to meet the needs of their transportation departments. If this project is implemented it can save agencies millions of dollars in resource development and reduce the time to see safe, efficient and effective green streets implemented across the country.

Related Research:

In 2008 the EPA published a Green Street handbook for municipalities documenting typical green stormwater strategies, implementation challenges and case studies but this handbook does not include design guidance. Similarly, the Institute of Transportation Engineers (ITE) “Designing Walkable Urban Thoroughfares: A Context Sensitive Approach” recommends integrating sustainable stormwater practices into the roadway and introduces general concepts and benefits. However, the report does not discuss or provide guidance for how Green Streets can be designed to minimize impacts to pedestrian access, on-street parking, or roadside safety. This is, how the depth, length, edge conditions, and marking of GSI facilities impact all users (pedestrians, bicyclists, drivers) of the roadway. The recent National Association of City Transportation Officials (NACTO) Urban Street Design Guide also recommends the use of GSI, recognizing the many co-benefits of integrating GSI into the roadside. These documents highlight the direction that street and its associated stormwater design are headed but they do not provide adequate design guidance.

Sponsoring Committee:AFB40, Landscape and Environmental Design
Research Period:24 - 36 months
Research Priority:High
Date Posted:01/15/2019
Date Modified:02/06/2019
Index Terms:Performance measurement, Best practices, Streetscape, Streets, Runoff, Detention basins, Drainage structures, Drainage practices,
Cosponsoring Committees: 
Subjects    
Highways
Design
Environment

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