SR 509 Completion Project

Extending SR 509 will ease congestion on I-5 near Tukwila, 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. WSDOT will complete SR 509 by building four new lanes between South 188th St. and its connection with I-5 at South 221st St. 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.