SR 509 Completion Project

Project news

  • We recently held a meeting for contractors interested in constructing our Stage 1b project, which includes building the new SR 509/I-5 interchange and improving the SR 516/I-5 interchange. This brings us one step closer to starting construction, scheduled to begin in mid-2020. 
  • In early 2020, Sound Transit will begin constructing the Federal Way Link Extension Project. As part of that work, Sound Transit’s contractor will also build a bridge for WSDOT. The bridge will make it possible for the new SR 509 to travel under SR 99 and the light rail guideway.
  • We have now acquired over 65 percent of the needed right of way for the planned improvements. If you have specific questions about property to be purchased for the SR 509 Project, please contact Jason Motland, the SR 509 Project real estate manager, at or 206-805-2819.
  • We have posted updated information about our Stage 1b Design-Build Project on the Ad and Award Website.

Needs & benefits

Check out our video about the SR 509 Project to learn about the project’s benefits and get a glimpse of what it will look like when it’s completed.

Extending SR 509 will ease congestion on I-5 near Tukwila, add a southern access point to Sea-Tac International Airport, and improve service between industrial districts by allowing general purpose traffic and trucks to bypass I-5, SR 99 and local streets.

When finished, SR 509 will become a key component of the Seattle and south King County transportation network. When considered in conjunction with the planned Alaskan Way Viaduct improvements, the project provides a critical north-south corridor alternative to I-5 through Seattle and South King County.

  • Freight connections. Completes critical freight links between the Port of Seattle and key distribution, warehouse and industrial centers in King County.
  • Regional mobility. Reduces traffic congestion on local roads and highways by completing connections between Seattle and the Kent Valley. Provides an alternate route to I-5 in south King County. 
  • Airport Access. Provides for a new connection between I-5 and Sea-Tac Airport from the south for both passengers and air cargo.
  • Regional job and economic growth. Supports regional job growth and economic growth associated with the state's two largest ports.
  • Intelligent transportation. Improves safety and manages congestion with tolling.
  • Advance wetland mitigation. Improves water quality and wildlife habitat by completing environmental improvements in advance of the project.


  • We have partnered with King County to build a 2.2 mile section (Segment C) of the Lake to Sound Trail in SeaTac and Burien. Once completed, the trail will provide a 16-mile non-motorized, multi-use connection between Lake Washington in Renton and the Puget Sound in Des Moines.
  • As part of our partnership with Sound Transit, their Federal Way Link Extension contractor will build Stage 1a of the SR 509 Project for us. This arrangement will reduce community impacts and help keep us on schedule. Sound Transit expects to begin construction in fall 2019.


The SR 509 Completion Project was originally funded over a 16-year timeline with targeted completion in 2031. The new timeline, which is a result of the State Legislature advancing the Program funding, anticipates project completion in 2028. Based on the funding plan under Connecting Washington, the first stage of construction consists of a new bridge over SR 99 near South 208th Street; work begins in late 2019 and will take about two and a half years to complete. Stage 1b, which includes reconstructing the I-5/SR 516 interchange and a new South 216th Street I-5 overpass, will be constructed between 2020 and 2025. Stage 2, which includes the majority of the new SR 509 construction and improvements to I-5 between SR 516 and South 272nd Street, will be constructed between 2024 and 2028.


The SR 509 Completion Project is funded as part of the Puget Sound Gateway Program. The total cost of the Puget Sound Gateway Program is $1.96 billion; $1.57 billion will come from the Connecting Washington Revenue Package, tolling revenue is expected to be $180 million, and local contributions will be $130 million. The SR 509 Completion Project will receive about $900 million of the Program’s total funds.


Chris Hoffman
Public Information

Susan Everett
Project Manager

Andrey Chepel
Project Engineer

SR 509 Completion Project map thumbnail