People driving on South 200th Street in SeaTac should expect nightly closures for three consecutive weeks, beginning the week of Aug. 17, according to the Washington State Department of Transportation (WSDOT).

The street will close from 8 p.m. to 5 a.m., Monday through Saturday, so WSDOT contractor crews can allow large trucks to safely cross South 200th Street to haul in soil needed to build the new State Route 509 Expressway.

This work is part of the SR 509 Completion Project.

South 200th Street closure information

Monday, Aug. 17 to the morning of Saturday, Aug. 22:

  • 8 p.m. to 5 a.m. – South 200th Street will close nightly in both directions between 18th Avenue South and just east of the Des Moines Creek Trail. Signed detours will be in place.

Monday, Aug. 24 to the morning of Saturday, Aug. 29:

  • 8 p.m. to 5 a.m. – South 200th Street will close nightly in both directions between 18th Avenue South and just east of the Des Moines Creek Trail. Signed detours will be in place.

Monday, Aug. 31 to the morning of Saturday, Sept. 5:

  • 8 p.m. to 5 a.m. – South 200th Street will close nightly in both directions between 18th Avenue South and just east of the Des Moines Creek Trail. 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 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.