When heavy rain falls on the Washington region, the runoff from impermeable surfaces like roadways and sidewalks can carry trash, sediment, oil, bacteria, and other road-related pollutants into nearby waterways like the Potomac and Anacostia rivers, and eventually into the Chesapeake Bay.
A new regional "Green Streets" policy, approved by the Transportation Planning Board at its February meeting, encourages state and local jurisdictions across the region to take steps to reduce the volume of water that runs off into streams, or to slow the rate at which it does.
The regional Green Streets policy calls for the use of planted vegetation and other "green" treatments like permeable pavement materials and rain gardens along roadways to reduce or slow runoff. These treatments serve as natural filters to stop pollutants before they enter storm drains, which can be a more cost-effective alternative to traditional engineering approaches, such as channeling stormwater to centralized facilities for processing. Reducing runoff volumes and rates can also lessen the frequency and severity of flooding, especially localized flash flooding during heavy rains.
Beyond these benefits, Green Streets treatments also beautify streets, making them more welcoming places to walk or bicycle. The shade and natural cooling effects that street trees and other vegetation provide make streets more comfortable places to be during hot summer months, reduce air-conditioning costs for nearby buildings, and moderate the urban heat island effect.
The regional policy approved by the TPB specifically encourages local jurisdictions to adopt Green Streets policies, or to revise existing ones, to include key best practices that the TPB and its stakeholders have agreed are essential elements. Those best practices are outlined in the policy, as is a resource guide including policies, guidebooks, standards, and manuals from other agencies and organizations around the country.
In the Washington region, many jurisdictions already have Green Streets policies in place, including Arlington and the District of Columbia. Prince George's County adopted a Green Streets policy in 2012 requiring all County-financed road, sidewalk, trail, and transit projects to include environmental site design elements to reduce runoff from heavy rains. The County is currently in the process of converting excess sidewalk space along Ager Road into bioswales, which use tall grass, rocks, and soil to collect and filter rain water.
The TPB began developing the regional Green Streets policy in December 2012 in response to a request from the Anacostia Watershed Restoration Partnership. In April 2013, the TPB convened a workshop of more than 90 staff from area transportation and environmental agencies or other interested individuals to discuss the challenges and opportunities associated with implementing Green Streets treatments.
Later this year, the TPB will hold another workshop to provide training on Green Streets best practices. The TPB will also conduct periodic surveys of area jurisdictions to assess the degree to which Green Streets policies have been adopted and implemented at the local and state level.
The Transportation Planning Board's recent approval of a regional Green Streets policy complements its ongoing work, including the May 2012 adoption of a regional Complete Streets policy, to make area roadways safer and more inviting for more people, especially pedestrians and bicyclists, and to do so in ways that help protect and enhance the region's natural environment.