A celebration of connections marks the final stage of SR 509 construction in South King County

SR 509 Completion Project will connect the 50-year-old highway to I-5

SEATAC - Community, industry and elected leaders joined together in SeaTac on Wednesday, Sept. 25, to celebrate the beginning of construction on the final stage of the State Route 509 Completion Project in south King County.

The project builds 3 miles of new tolled expressway that connects SR 509 to Interstate 5. The expressway is being built in two major stages. The first stage is already under construction and is building 1 mile of highway between I-5 and 24th Avenue South in SeaTac. It will open in 2025. The final stage builds the remaining 2 miles between 24th Avenue South and South 188th Street, where it will connect to the existing portion of SR 509. It will be complete in 2028.

"Providing a safe, sustainable, integrated and resilient transportation network is key to our future," said Washington State Department of Transportation Secretary Roger Millar. "The SR 509 Completion Project is another step in that direction. We're building more than a highway; we're also creating multimodal options including trails and shared-use paths that will allow people to connect more easily to local jobs, businesses and neighbors in support of vibrant and thriving communities."

The SR 509 Completion Project is being built in close coordination with local cities and transit agencies with an eye toward complementing local land use plans that encourage employment opportunities and housing near multimodal transportation options.

"This project completes critical connections to our regional trail system and public transportation, including Sound Transit's light rail extension to Federal Way," said Sen. Marko Liias. "This will support mobility on I-5 and enhance the movement of freight for our entire Puget Sound region."

"The city of SeaTac is a designated regional growth center and Sea-Tac Airport is a growth driver," said Mayor Mohamed Egal. "Connecting SR 509 to I-5 allows us to continue to support existing businesses and attract new ones."

During the celebration event, area leaders from government, transit, freight and development stood shoulder-to-shoulder holding signs with project features such as "ADA-accessible paths," "direct connection to the port," and "less congestion on local roads" to create a visual ribbon of benefits that the SR 509 expressway will bring to the region.

"This project, along with the completion of SR 167 in Pierce County, supports both local and regional economies and creates living wage jobs," said Rep. Jake Fey. "The collaboration with our local partners, the ports, and the community means we can move cargo more efficiently through the airport and our seaports in Tacoma and Seattle."

SR 509 expressway highlights

When complete, the 3-mile tolled expressway will have two lanes in each direction between I-5 and South 188th Street, with a southbound on-ramp and northbound off-ramp at 24th Avenue South. A new interchange at South 188th Street will connect the new expressway to the existing portion of SR 509. The older section of SR 509 will not be tolled. The project also builds new roundabouts to maintain traffic flow at the SR 509 interchange with South 160th Street in Burien and new noise walls in select locations.

Improvements are also occurring on I-5, and even under it, as part of the project. Crews are reconfiguring the interchange at SR 516 and building the new Veterans Drive tunnel under I-5, just north of the SR 516 interchange. Veterans Drive will be extended from Military Road South to the new tunnel, providing freight with more direct routes between the Kent Valley industrial center and I-5. Other improvements include a northbound I-5 flyover ramp to SR 509, a wider South 216th Street bridge over the interstate, a southbound I-5 auxiliary lane between SR 516 and South 272nd Street and new noise walls in several locations on I-5 and SR 509.

The project adds more than 5 miles of sidewalks and shared-use paths, including a 1.8- mile-long section of the Lake to Sound Trail.

Puget Sound Gateway Program overview

The SR 509 Completion Project is part of WSDOT's $2.69 billion Puget Sound Gateway Program, which also includes the SR 167 Completion Project in Pierce County. The two projects finish critical missing links in Washington's highway and freight network. Photos of SR 509 construction work are available in the project's Flickr albums. An interactive video that allows people to view project features is also available online.