Drivers should expect lane closures on I-5 in SeaTac Thursday, Mar. 26 to the morning of Friday, Mar, 27, according to the Washington State Department of Transportation (WSDOT).

This closure will allow contractor crews working for WSDOT to work on guardrail construction.

Guardrails add a protective barrier along the highway and help support safer travel by keeping vehicles from leaving the roadway.

This work is part of the SR 509 Completion Project.

I-5 lane closure information

Thursday, March 26 to the morning of Friday, March 27:

  • 10 p.m. to 6 a.m. – Up to two lanes of southbound I-5 will close overnight from South 200th Street/Military Road South (Exit 151) to SR 516 (Exit 149). The exit to SR 516 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 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.