SR 509 Completion Project


February 2018

On January 16, 2018 the Federal Highway Administration (FHWA) approved the National Environmental Policy Act (NEPA) Re-Evaluation of the SR 509 Completion Project.

To learn more about the Re-Evaluation and view more project information, please visit our online open house.

You may also view the Re-Evaluation online or visit one of the following local libraries:

  • Burien Library, 400 SW 152nd St, Burien, WA 98166
  • Valley View 17850 Military Rd S, SeaTac, WA 98188
  • Des Moines library, 21620 11th Ave S, Des Moines, WA 98198
  • East Kent Regional Library, 212 Second Ave N, Kent, WA 908032

The open house will be online for thirty days, and all comments on the Re-Evaluation should be submitted by February 22.

Why is WSDOT extending SR 509?
 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.

The End Result
WSDOT will complete SR 509 by building four new lanes between South 188th St. and its connection with I-5 at South 221st St.

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.

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 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.

What is the project timeline?
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 begin in 2022, and a second stage would begin in 2025/2026.

Financial Information

Financial Data for PIN 850901F, 850902A
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $34,993
2005 Gas Tax (TPA) $26,034
Pre-Existing Funds (PEF) $0
CWA $0
Total $61,027

This project received funding through the following sources:

  • 2005 Gas Tax -$30 million
  • 2003 Gas Tax - $35 million
  • Other funds - $21 million
    (from pre-existing state, federal and other partnerships)
  • 2015 Connecting Washington - $1.9 billion (shared between SR 509 and SR 167)


How can I get more information?

Omar Jepperson, P.E.
Project Manager

Emily Mannetti
Public Information

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