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SR 509, I-5 to 24th Avenue South – Expressway Project

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This online open house ran from November 13 to December 20, 2021. While the public comment window is now closed, WSDOT is keeping the information available for viewing. For construction questions, please contact us at


WSDOT is starting construction on the SR 509, I-5 to 24th Avenue South – Expressway Project (Stage 1b) in fall 2021. 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 (I-5).

How to participate

This online open house provides information about construction: its main work zones and the schedules for completing the major activities. Please visit each page to learn more about the project and to make any comments on the Comments Page. We also hope you will take a few minutes to complete a brief survey at the end of the open house.

This online open house will remain active between November 13 to December 20, 2021.

What is the SR 509 Completion Project?

The SR 509, I-5 to 24th Avenue South – 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. People traveling through the area will have a new southern route to get to Sea-Tac International Airport and be able to bypass I-5, SR 518, and local streets. Community members will experience fewer container trucks on local roads as freight drivers will have a new route to access the airport. Along with the SR 99 tunnel improvements, travelers in the area will have access to a critical north-south alternative to I-5 through Seattle and King County.

A map of the SR 509 Stage 1b project
The project provides new options for all travelers, including new access to I-5 from Veterans Drive and new access to Sea-Tac International Airport via the SR 509 Expressway.