The State Route 509 Completion Project extends SR 509 to Interstate 5 near SeaTac and adds a southern access point just south of Sea-Tac International Airport.   The freeway extension will improve service between industrial districts by allowing general-purpose traffic and trucks to bypass I-5, State Route 99 and local streets.

Besides regional mobility and regional economic growth, benefits of this project include a new South 216^th Street overpass that will provide pedestrian and bike access, improvements for South 208^th Street, a new street (34^th Ave South from South 204^th Street to South 208^th Street), and funding for a portion of the Lake to Sound Trail from SeaTac to Burien.

$1 billion in funding for the SR 509 Completion Project comes from the Connecting Washington funding package, local contributions, tolling, and federal grants.

Schedule 

This project is targeted for completion in 2028. Phase 1A, the new SR 99 Bridge near South 208^th Street is targeted for completion in 2022.

The design build contract for Phase 1B (the expressway from24th Avenue South to Interstate 5) has been awarded; construction is anticipated to begin in 2022.

View the latest Construction Presentation

Additional information can be found on the project webpage:   

 https://wsdot.wa.gov/construction-planning/search-projects/sr-509-completion-project