Drivers should expect nighttime closures of South 188th Street in SeaTac Monday, Oct. 26 to the morning of Wednesday, Oct. 28, the Washington State Department of Transportation (WSDOT) announced.

These closures will allow WSDOT contractor crews to set large support beams for a future SR 509 Expressway bridge. When complete, the bridge will cross over South 188th Street/Des Moines Memorial Drive South and connect the existing SR 509 to the new expressway.

This work is part of the SR 509 Completion Project.

South 188th Street closure information

Monday, Oct. 26 to the morning of Wednesday, Oct. 28:

  • 9 p.m. to 4 a.m. – South 188th Street will close in both directions between Des Moines Memorial Drive South and 8th Avenue South. Signed detours will be in place. The on- and off-ramps to SR 509 will remain open.

SR 509 Completion Project information

The SR 509 Completion Project builds 3 miles of new tolled highway between I-5 and South 188th Street near the south end of Seattle-Tacoma International Airport. The new highway will be completed in stages. The first mile between I-5 and 24th Avenue South opened in June 2025. Construction of the final 2 miles between 24th Avenue South and South 188th Street is underway and currently scheduled to open to traffic in July 2028.

Puget Sound Gateway Program overview

The SR 509 Completion Project is part of WSDOT’s Puget Sound Gateway Program, which also includes the SR 167 Completion Project in Pierce County. Together, the two completion projects finish critical missing links in Washington’s highway and freight network.