Road Services - Low Impact Development (LID) for roads
Military Road South at South 272nd Street Project
"Green Building for Transportation Infrastructure"
This is an intersection improvement project located at Military Road South at South 272nd Street, which received a Washington State Department of Ecology (DOE) Low Impact Development (LID) stormwater grant. The grant of $424,375 enables King County to fund the following activities: The construction of porous concrete sidewalks and a bioretention facility/rain garden. The development and implementation of a monitoring program to monitor the performance of the sidewalks and bioretention facility for a period of 3 years after construction. The development of public outreach and educational measures to share knowledge about the low impact development components of this project (e.g., interpretive signage at the project site, a website, project tours, public presentations, and writing articles for publication).
Non-Low Impact Development components of this project include:
- Construct an eastbound right turn lane and add an additional northbound left turn lane.
- Construct sidewalks that will reduce the project’s overall impervious area.
- Existing traffic signal and traffic cameras will be upgraded.
About Low Impact Development
Low Impact Development is an approach to land development and stormwater management that emphasizes conservation, retention, and infiltration through the use of distributed, small-scale facilities integrated with natural features. In contrast to the typical approaches to stormwater management, the primary goal of Low Impact Development is to mimic natural hydrology by managing stormwater at its source. Low Impact Development designs typically focus on reducing impervious surfaces and maximizing on-site stormwater detention, infiltration, and evaporation.
Learn more about Low Impact Development:
- King County, Washington
- Puget Sound Action Team
- Low Impact Development Technical Guidance Manual
- Washington State Department of Transportation
- Washington State Department of Ecology
- U.S. Environmental Protection Agency
What are some reasons for using Low Impact Development on this project?
- Reduces the amount of new impervious surface.
- Helps maintain natural hydrology.
- Helps protects Star Lake and nearby wildlife habitat from high storm flows.
- Lowers the cost of stormwater infrastructure by eliminating the need for a stormwater vault or large R/D pond.
- Improves the appearance and aesthetics of the roadway.
What makes this project green?
Low Impact Development approaches such as the porous cement concrete sidewalks and the bioretention stormwater facility/rain garden make this a "green" project. Although Low Impact Development approaches have been widely applied to residential streets, this project demonstrates the potential for utilizing Low Impact Development approaches in the more alternative context of larger scale transportation infrastructure projects.
To fulfill grant requirements, the project will monitor the performance of the "green" aspects of the project, including the porous sidewalks and bioretention facility, for three years after construction.
- Construct 1,100 square yards of porous concrete sidewalks.
- The rain garden is 285’ long and covers 0.12 acres.
- Construction cost is $1.1 million.
- Department of Ecology (DOE) grant in the amount of $424,000.
- Transportation Improvement Board (TIB) grant in the amount of $640,000.
Related project documents
Low Impact Development Stormwater Grant Agreement Between the State of Washington Department of Ecology and King County (1MB .pdf)
This project is sponsored by the Washington State Department of Ecology, the Washington State Transportation Improvement Board, and King County.
For information about this project, please contact:
Jim Sussex, Engineer III
King County Road Services Division
Engineering Services Section, Environmental Unit
Information from the Road Services Division's website is available to people with disabilities in alternate formats upon request by calling 206-477-3839 or 711 for the TTY relay service.
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