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SR 509 completion project


January 2018

The SR 509 Steering and Executive committees met regularly with the SR 167 Steering and Executive committees throughout the past 18 months. These groups reviewed design options, technical analysis and funding options for the project. You may view the preliminary preferred scenario and other information in our latest project folio.

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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