Drivers should expect nightly lane closures on SR 509 in SeaTac Monday, July 6 to the morning of Friday, July 10, according to the Washington State Department of Transportation (WSDOT).

These closures will allow contractor crews working for WSDOT to perform electrical work.

This work is part of the SR 509 Completion Project.

SR 509 lane closure information

Monday, July 6 through the morning of Friday, July 10:

  • 8 p.m. to 5 a.m. – One lane of northbound SR 509 will close nightly from South 176th Street to South 160th Street.

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.