• Project

SR 509 Completion Project

Project overview

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.

Timeline
2015-2028
Project status
Construction
Funding
$2.38 billion funds both the SR 509 Completion Project in King County and the SR 167 Completion Project in Pierce County.
Project hotline

What to expect

Construction on Stage 1a and Stage 1b of the project is currently underway. 

SR 516/I-5 Interchange: Through January 2023, construction crews will construct a temporary off-ramp to SR 516 from southbound I-5. Expect both daytime and nighttime construction, with night lane reductions on I-5.

Northbound I-5, from SR 516 to the vicinity of South 211th Street:  Through January 2023, Crews will widen northbound I-5, adding new drainage pipes, asphalt, concrete barriers, and bridge piers on the east side of I-5. The piers will eventually support a widened bridge at South 216th Street and a new overpass for SR 509.

Southbound I-5, from Military Road to SR 516: Through January 2023, construction crews will continue construction on a new southbound I-5 collector-distributor lane and ramp, as well as new bridge piers on the west side of I-5. The piers will eventually support a widened bridge at South 216th Street and a new overpass for SR 509.

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).