Performance Measures, Best Practices and Recommended Design Guidance for Green Streets
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.
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
● Identify ongoing research and initiatives for the
planning, design and implementation of Green Streets.
● Identify future research needs and opportunities for
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
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|
|Index Terms:||Performance measurement, Best practices, Streetscape, Streets, Runoff, Detention basins, Drainage structures, Drainage practices, |