May the detours be with you, SeaTac. South 200th Street will close nightly from Monday, May 4 to the morning of Thursday, May 7, the Washington State Department of Transportation (WSDOT) announced.

This closure will allow WSDOT contractor crews to set 16 bridge girders for the SR 509 Expressway’s flagship bridge.

When complete, the bridge will be 1,587-feet-long and cross over the Des Moines Creek wetland, South 200th Street and the Lake to Sound Trail.

This work is part of the SR 509 Completion Project.

South 200th Street closure information

Monday, May 4 to the morning of Thursday, May 7:

  • 9 p.m. to 4 a.m. – South 200th Street will close nightly in both directions between 18th Avenue South and Des Moines Creek Trail. A signed detour will be in place.

About the girders

Bridge girders are horizontal beams that support the weight of the bridge and form the foundation of the bridge deck. Spanning between piers, these girders will carry the new structure over South 200th Street. Fun fact: If all 16 girders were stacked end‑to‑end, they would be taller than four Space Needles.

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 portion between I-5 and 24th Avenue South opened on June 28, 2025 and a new tunnel under I-5 at the SR 516 interchange opened on July 16, 2025. The final stage builds the remaining 2 miles of the expressway between 24th Avenue South and South 188th Street. The entire project is planned for completion by 2029.

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.