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SR 509, I-5 to 24th Avenue S. – New Expressway Project

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This online open house ran from January 25 to March 5, 2021. While the public comment window is now closed, WSDOT is keeping the information available for viewing. For construction questions, please contact Chris Hoffman,


WSDOT is starting construction on the SR 509, I-5 to 24th Avenue S. – Expressway Project in 2022. This project is part of WSDOT’s effort to extend the SR 509 highway from where it currently ends by Sea-Tac International Airport to Interstate 5.

How to participate

This online open house details the project’s key features and benefits. It also provides an opportunity to share your feedback. Please visit each page to learn more about the project and make any comments on the Comments and Survey Page. We also hope you will take a few minutes to complete the brief survey on that same page.

This online open house will remain active between January 25 and March 5, 2021.

What is the SR 509 Completion Project?

The SR 509, I-5 to 24th Avenue S. – Expressway Project is part of the greater SR 509 Completion Project, scheduled for completion in 2028. The SR 509 Completion Project will ultimately extend SR 509 to I-5 in SeaTac and add a southern access route to Sea-Tac International Airport to allow drivers to bypass I-5, SR 518, and local streets.

When finished, SR 509 will provide new access to the airport and will help get freight off local streets. Along with the SR 99 tunnel improvements, WSDOT will provide a critical north-south alternative to I-5 through Seattle and King County.

A map of the three stages of the SR 509 completion project
The project will improve access through the area with interchange improvements, new ramps that connect I-5 to SR 509, and the first mile of the SR 509 Expressway. Stage 2 of the project will complete the connection between 24th Avenue South and South 188th Street (where SR 509 currently ends).