As the Washington region continues to grow, new development, roadway construction, and vehicle travel will increasingly impact the region's natural environment. An approach to roadway design known as Green Streets could help mitigate some of those impacts, especially the effects of excess runoff from heavy rains on local streams and other waterways.
Over the last few months, the Transportation Planning Board has been working with jurisdictions from across the region to explore the idea of developing a regional Green Streets policy. The work follows the TPB's approval in May 2012 of a regional Complete Streets policy encouraging local jurisdictions to promote the safe accommodation of multiple transportation modes when designing new roadways and making major improvements to existing ones.
Green Streets design principles focus on mitigating the impact of stormwater runoff by strategically placing trees and other plants adjacent to roadways to reduce the volume of water that runs off into streams or to slow the rate at which it runs off.
High volumes of runoff can increase the frequency and severity of floods and contaminate water supplies by carrying debris and other road-related pollutants into streams and other bodies of water. As communities throughout the region continue to develop, they will require construction or installation of more and more surfaces – like roofs, sidewalks, and streets – that traditionally have led to increased runoff.
Among the techniques used when building or retrofitting Green Streets are planting street trees, replacing concrete medians and unnecessarily wide sidewalks with planted vegetation, and using permeable concretes and other surfaces that allow water to sink through the pavement and into the soil. The vegetation and soil both act as a natural filter of debris, sediment, oil, and bacteria.
Such approaches can provide a cost-effective alternative to traditional engineering solutions that channel water to processing plants or bodies of water. The additional vegetation that often accompanies Green Streets approaches can also improve air quality and reduce heat in urban areas, and the improved aesthetics of Green Streets can increase nearby property values.
The TPB began studying the possibility of adopting a Green Streets policy in December 2012 after the Anacostia Watershed Restoration Partnership requested that the TPB do so. The TPB subsequently hosted a stakeholder workshop attended by more than 90 staff from area transportation agencies as well as other interested individuals.
At the workshop, representatives from the U.S. Environmental Protection Agency and several local jurisdictions gave presentations highlighting best practices for Green Streets implementation. Workshop participants discussed some of the challenges that arise in implementing Green Streets, including working with utilities companies to relocate power and other utility lines, negotiating with property owners about access to change the right of way, and ensuring compatibility with existing drainage systems.
Some planners and decision-makers have expressed concern that retroactively converting existing roads to Green Streets could be very expensive. Variations in local conditions and needs, including limited space for existing road users, could also stand in the way of making Green Streets improvements.
In order to be successful, participants also noted that Green Streets policies require a high level of cooperation between multiple government agencies that manage transportation, planning, and the environment as well as with developers who often implement Green Streets elements during construction.
A number of jurisdictions in the area have already adopted Green Streets policies, including Arlington and the District of Columbia. Prince George's County adopted a Green Streets policy in conjunction with its Complete Streets policy, requiring that all County-approved and -financed road, sidewalk, trail, and transit projects include environmental site design elements to reduce runoff from heavy rainfalls. As an example, the County is converting excess sidewalk along Ager Road into bioswales that use tall grass, rocks, and soil to collect and filter rain water.
TPB staff is currently working with jurisdictions to study best practices and develop options for regional approaches to a Green Streets policy.
Reducing stormwater runoff is a long-term process, and by considering a Green Streets policy, the TPB is helping jurisdictions identify strategies that can make transportation networks in the region more environmentally-friendly.