The SR 509 Completion Project in King County is part of the Puget Sound Gateway Program, which also includes the SR 167 Completion Project in Pierce County. Together, these projects complete two of the Puget Sound region’s most critical freight corridors and improve access to I-5, the ports of Tacoma and Seattle and Seattle-Tacoma International Airport. The SR 509 Completion Project builds a new four-lane expressway between I-5 and SR 509's current end near Sea-Tac Airport, builds new I-5 ramps, improves I-5 interchanges in south King County and constructs new bridges. When complete, the project will create an important north-south alternative to the congested I-5 corridor between Seattle and south King County.
What to expect
Closures for South 216th bridge demolition
The South 216th Street bridge over I-5 in SeaTac will be demolished Dec. 8-9.
8:30 p.m. Thursday, Dec. 7: Both directions of South 216th Street between Military Road South and 31st Avenue South close for pre-demolition bridge work. Drivers will follow signed detours. When it reopens at 5:30 a.m. Friday, Dec. 8, eastbound traffic on South 216th Street will use signed detours to cross I-5 until mid-2024. Westbound South 216th Street traffic will cross I-5 using the southern portion of the new bridge.
10 p.m. Friday, Dec. 8 to 8 a.m. Saturday, Dec. 9 - All lanes of southbound I-5 are closed at South 200th Street.
10 p.m. Saturday, Dec. 9 to 8 a.m. Sunday, Dec. 10 - All lanes of northbound I-5 are closed at SR 516.
9 p.m. to 9 a.m., nightly, Friday, Dec. 8 and Saturday, Dec. 10 - Both directions of South 216th Street between Military Road South and 31st Avenue South closed.
The SR 509 Completion Project builds three new miles of SR 509 and completes the unfinished SR 509 in south King County. This new four-lane highway will become an important north-south alternative to the congested I-5 corridor between Seattle and south King County. The new segment of SR 509 will be called an expressway and will be tolled at one electronic toll point (no tollbooths).