SR 509 Completion Project

Project news

  • After the passage of I-976 in the Nov. 5 election, Gov. Inslee directed WSDOT to pause a number of planned projects that were not yet under construction. The SR 509 Stage 1b Project is on the postponed project list (pdf 256 kb), however preliminary engineering and property acquisition will continue. Through the Request for Qualifications process, WSDOT has already shortlisted three design-build teams for the Stage 1b contract. The contractor selection process is on hold until the 2020 Legislature concludes in the spring and provides further direction.
  • Our Stage 1a project is heading into construction! We have a construction agreement with Sound Transit for their contractor, Kiewit, to begin construction on our Stage 1a project in 2020 as part of their Federal Way Link Extension. The Federal Way Link Extension will extend light rail from Angle Lake Station to the Federal Way Transit Center in the same area as our Stage 1a project, which includes a new SR 99 bridge to make room for the future SR 509 extension. Visit Sound Transit’s website to learn more about the project.
  • We conducted a survey in early 2019 to understand how pedestrians might be affected by construction to widen the South 216th Street Bridge over I-5, which begins in 2021. We learned several residents rely on the bridge to get to and from their destinations on foot. Because of that, we changed our original plan to restrict pedestrian access across the bridge and will keep the bridge open to pedestrians throughout construction.

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