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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 International Airport to I-5. While the new expressway is only three miles long, the project is much bigger, including 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.

Based on current designs, this project introduction video points out key features and benefits of the SR 509 Completion Project. Final design may vary from the visualization pictured here.

Project timeline

The SR 509 Completion Project is already under construction. Stage 1a and Stage 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.

The SR 509 project timeline. Stage 1a ends in 2022. Stage 1b ends in 2025. Stage 2 ends in 2028. Tolling begins late 2025.
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 in late 2024.