SR 509 Completion Project

Project news

  • On January 16, 2018 the Federal Highway Administration (FHWA) approved the National Environmental Policy Act (NEPA) Re-Evaluation of the SR 509 Completion Project.
  • The Re-Evaluation is available on a project online open house. Members of the public were also welcome to comment on the Re-Evaluation for 30 days. Read a summary of responses to the comments we recieved (pdf 375 kb)

Needs & benefits

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.


SR 509 was funded over a 16-year timeline. Based on the funding plan under Connecting Washington, major construction for the first stage would likely occur in 2022-2025, and a second stage would begin in 2026-2029.


  • Connecting Washington: $1,565 million
  • Local Funding: $130 million
  • Toll Funds: $180 million
  • Total funding:  $869 million


Andrey Chepel, P.E.
Project Manager

Amy Danberg
Public Information

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