Drivers should expect nighttime lane closures on South 188th Street in SeaTac starting this Saturday, July 18 through the morning of Sunday, July 19, and again Monday, July 20, through the morning of Tuesday, July 21.

These closures will allow Washington State Department of Transportation contractor crews to demolish the current bridge over South 188th Street to make room for a new one.

This work is part of the SR 509 Completion Project.

South 188th Street closure information

Saturday, July 18 to the morning of Sunday, July 19:

  • 8 p.m. to 8 a.m. – South 188th Street will close in both directions from Des Moines Memorial Drive South to 8th Ave South. Signed detours will be in place.

Monday, July 20 to the morning of Tuesday, July 21:

  • 8 p.m. to 8 a.m. – South 188th Street will close in both directions from Des Moines Memorial Drive South to 8th Ave South. Signed detours will be in place.

SR 509 Completion Project information

The SR 509 Completion Project builds 3 miles of new tolled highway between I-5 in SeaTac and South 188th Street near the south end of Seattle-Tacoma International Airport. Crews are building the new expressway in stages. The first stage, completed in 2022, built a new bridge on SR 99 in SeaTac. The next stage, which opened in summer 2025, built the first mile between I-5 and 24th Avenue South. That stage also included the new Veterans Drive tunnel in Kent near the SR 516 interchange.

Crews are now working on the final stage which builds the remaining 2 miles of the expressway between 24th Avenue South and South 188th Street in SeaTac. The entire expressway is scheduled to open to the public in 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 projects complete critical missing links in Washington’s highway and freight network.