This page describes project key features. The designs presented are conceptual. The design-builder will finalize schedules and designs, which may vary from the conceptual designs.
During project development, construction, and beyond, WSDOT is committed to the safety, health, and quality of life of nearby communities. This page highlights how the SR 509, 24th Avenue South to South 188th Street – New Expressway Project will address three major concerns that we have heard from our neighbors: multi-modal access, safety, and noise.
Multi-modal & pedestrian safety
Washingtonians use all sorts of methods to get from one place to another. With this in mind, project engineers designed interchanges and intersections within the new SR 509 expressway that improve safety and access for community members who walk, ride, and roll.
Wide sidewalks with traffic buffers on the South 160th Street overpass and new South 192nd Street bridge will enable safe crossing over SR 509. On the south side of South 188th Street, a separated multi-use path and clear signage at roundabout intersections will connect seamlessly to King County’s Lake to Sound muti-use trail.
But we’re not just completing SR 509. As part of this project, WSDOT is also providing funding for King County to build a critical missing link of the Lake to Sound multi-use trail. The 1.8-mile Lake-to-Sound Trail – Segment C (L2ST-C) project is already under construction and expected to be completed by spring 2023. Learn more by visiting King County Parks’ L2ST-C project page.
Following the 2003 environmental review process, changes to the roadway design resulted in a substantial reduction in anticipated noise increases for households, businesses, and public spaces bordering the SR 509 Completion Project. A major factor contributing to this noise reduction was the addition of tolling to the new SR 509 expressway, which allowed engineers to re-design a roadway with fewer lanes and less traffic.
Where traffic noise may rise above 65 decibels, WSDOT is building new noise walls and extending existing noise walls. For reference: a household refrigerator produces about 55 decibels, whereas a vacuum cleaner produces about 75 decibels.
In addition to more than 12,000 feet of new noise walls constructed in Stages 1a and 1b of the SR 509 Completion project, WSDOT will build two new noise walls and extend one existing noise wall during Stage 2. This includes:
- One new 874-foot noise wall located northeast of the new SR 509/South 160th Street interchange
- One new 1,180-foot noise wall located southwest of the new SR 509/South 160th Street interchange
- 230-foot extension of the existing noise wall located on the east side of I-5 just south of the Midway landfill