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SR 509 completion project


October 2017

  • 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, 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
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

  • Reduced Congestion. Fewer vehicles and less traffic on I-5 in South King County by providing an alternate north-south route to I-5.
  • Advanced wetland mitigation. Environmental improvements completed in advance of the project improve water quality and wildlife habitats for the Des Moines Creek basin.
  • Intermodal freight mobility. Creating a direct route for freight and general traffic movements to and from the Puget Sound marine ports and the industrial areas of Seattle and South King County.
  • Airport Access. Provides for a new connection between I-5 and Sea-Tac Airport from the south.
  • Public value. Reduces travel times between Seattle and Tacoma and between the Port of Seattle and the Kent Valley.
  • Intelligent transportation through tolling. In addition to adding revenue, creating a toll road will help manage travel demand to improve system performance.

What is the project timeline?
Funding through the Connecting Washington Account will be distributed over a 16 year period. WSDOT anticipates construction will be complete in 2030.

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?

Emily Mannetti, Public Information

Omar Jepperson, P.E.

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