Project overview
The SR 509 Completion Project in King County is part of the Puget Sound Gateway Program, which also includes the SR 167 Completion Project in Pierce County. Together, these projects complete two of the Puget Sound region’s most critical freight corridors and improve access to I-5, the ports of Tacoma and Seattle and Seattle-Tacoma International Airport. The SR 509 Completion Project builds a new four-lane expressway between I-5 and SR 509's current end near Sea-Tac Airport, builds new I-5 ramps, improves I-5 interchanges in south King County and constructs new bridges. When complete, the project will create an important north-south alternative to the congested I-5 corridor between Seattle and south King County.
What to expect
Construction on Stage 1b of the project is currently underway.
SR 516/I-5 interchange: Crews are working in the I-5 median to construct a new tunnel that will connect Veterans Drive to ramps on northbound and southbound I-5.
Southbound I-5, from South 220th to South 240th streets: New barrier-separated HOV lanes will allow crews to set girders for the new South 216th bridge and the new northbound collector-distributor flyover. Girders will be set over I-5 in June and July.
SR 509 corridor: Crews are excavating the new SR 509 expressway under the Sound Transit guideway and SR 99 bridges in SeaTac. Crews will relocate traffic from South 208th Street onto a new South 206th Street connection at International Boulevard. The new South 34th Street that connects South 204th and South 208th is underway and will open in July.
Southbound I-5 speed reduction: A temporary speed reduction to 50 mph is in place on southbound I-5 between milepost 150 near South 220th Street in Des Moines and milepost 149 near South 240th Street in Kent.
The SR 509 Completion Project builds three new miles of SR 509 and completes the unfinished SR 509 in south King County. This new four-lane highway will become an important north-south alternative to the congested I-5 corridor between Seattle and south King County. The new segment of SR 509 will be called an expressway and will be tolled at one electronic toll point (no tollbooths).
