SR 509 Completion Project

Project news

  • In accordance with Governor Inslee’s “Stay Home, Stay Healthy” order, WSDOT suspended construction on most of its projects statewide. Sound Transit recently halted work on many of its projects as well, including the FWLE light rail project. This suspension is in effect until at least May 4. Sound Transit’s light rail contractor is building the SR 99 bridge for the future SR 509 extension. Visit the Sound Transit  FWLE website to learn more about the project.
  • With the passage of the 2019/2021 supplemental transportation budget, projects that were paused due to the passage of I-976, including the SR 509 Completion Stage 1b Project, will now advance. As a result, we are resuming the SR 509 Stage 1b contractor selection process. We are on schedule to complete construction on the SR 509 1b project by the end of 2025.

Needs & benefits

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

The SR 509 Completion Project extends SR 509 to I-5 near Tukwila, adds a southern access point to Sea-Tac International Airport, and improves 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 be a key component of the Seattle and south King County transportation network. Along with the SR 99 tunnel improvements, the project provides a critical north-south alternative to I-5 through Seattle and King County.

Project benefits

  • 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 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. Electronic tolling on the route will manage congestion, which improves safety and reliability for all users.
  • Advance wetland mitigation. Improves water quality and wildlife habitat by completing environmental improvements in advance of the project.

Construction partnerships

  • We have contracted with King County to fund 1.8 miles the Lake to Sound Trail in SeaTac and Burien. Once completed, the trail will provide a 16-mile non-motorized, multiuse connection between Lake Washington in Renton and the Puget Sound in Des Moines.
  • As part of our construction agreement with Sound Transit, their Federal Way Link Extension contractor will build Stage 1a of the SR 509 Completion Project for us. This arrangement will reduce community impacts and help keep us on schedule. Sound Transit will begin construction in 2020.


The SR 509 Completion Project was originally funded over a 16-year timeline with targeted completion in 2031. The state Legislature advanced Program funding in the 2019 session, moving project completion to 2028.

  • Stage 1a: Constructs 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: Reconstructs the I-5/SR 516 interchange, improves I-5 to SR 509, constructs new interchange at 24th Avenue, and a constructs a new South 216th Street I-5 overpass between 2020 and 2025.
  • Stage 2: Constructs the majority of the new SR 509, improvements to I-5 between SR 516 and South 272nd Street between 2024 and 2028.


Gateway Program funding totals $1.96 billion from four sources: 1) $1.57 billion from the Connecting Washington funding package; 2) $130 million from local contributions; 3) $180 million from tolling; and 4) WSDOT is seeking federal grant funding. 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