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Spring 2022 – SR 509 Completion Project Online Open House – Project Introduction

What is the SR 509 Completion Project?

The SR 509 Completion Project extends the SR 509 highway from where it currently ends at the southeast corner of Sea-Tac airport to I-5. While the new expressway is only three miles long, the project is much bigger, improving traffic flow, multi-modal community connectivity, and environmental improvements that extend from South 160th Street in Burien all the way to South 272nd Street in Federal Way.

When finished, the SR 509 Completion Project will provide new access to Sea-Tac airport and regional seaports, help get freight off local streets, improve pedestrian safety, and improve travel times and roadway safety in south King County by offering a north-south alternative to I-5.


Project timeline

The SR 509 Completion Project is already under construction. Stage 1a and 1b activities include construction of the first mile of the new SR 509 expressway, new ramps and bridges connecting SR 509 to I-5 near South 212th Street, a new SR 509/24th Avenue South interchange, a reconfigured interchange at I-5/SR 516, and the construction of new and extended noise walls.

Stage 2 is nearing the end of its conceptual design phase, with the team preparing documents that will inform contractor bidding in 2023. Stage 2 construction activities are scheduled to begin in late 2024 and end by 2029.

A timeline of the SR 509 completion project and it's stages
Stages 1a and 1b are currently under construction. In 2023, WSDOT will select a design-build contractor for Stage 2 who will complete final design in 2024 and begin major construction by 2025.