South King County marked a major transportation milestone on Sept. 25 as community leaders gathered to launch construction on the last segment of the State Route 509 Completion Project. Designed to link SR 509 directly to Interstate 5, this infrastructure endeavor promises to ease traffic flow and enhance regional connectivity. According to the Washington State Department of Transportation (WSDOT), the new 3-mile tolled expressway will incorporate two stages, with an anticipated completion in 2028.
The initial stage, already underway, aims to swiftly build a 1-mile highway stretch between I-5 and 24th Avenue South in SeaTac, slated to open in 2025. The concluding segment will extend the remaining 2 miles to South 188th Street, culminating in a connection with the existing SR 509 road. "Providing a safe, sustainable, integrated and resilient transportation network is key to our future," WSDOT Secretary Roger Millar told WSDOT. Millar highlighted the multifaceted nature of the project, emphasizing its role not only as a highway but as a catalyst for multimodal transportation options that will bolster community ties.
Local cities, transit agencies, and the state department have closely collaborated to ensure that the project aligns with local land use plans that promote employment opportunities and housing in proximity to mixed transportation options. Senator Marko Liias celebrated the project for its enhancement of the regional trail system and public transport networks, including the forthcoming Sound Transit light rail extension to Federal Way. Liias expressed confidence in the project's capabilities to improve mobility and support the flow of freight in the Puget Sound region.
SeaTac Mayor Mohamed Egal underscored the strategic importance of the city as a regional growth center, citing the project's potential to bolster local businesses and attract new enterprise. During the kickoff event, leaders across government and industry sectors stood united, bearing signage that illustrated the myriad benefits of the SR 509 expressway — from ADA-accessible paths to smoother, less congested local routes.
Spanning 3 miles once complete, the tolled expressway will feature two lanes in each direction, new interchanges, and roundabouts meant to sustain efficient traffic flow. The undertaking is extensive, touching upon additional components such as reconfiguring I-5's SR 516 interchange and creating new avenues for freight transportation. Moreover, the project includes over 5 miles of sidewalks and shared-use paths, manifesting a tangible commitment to pedestrian and cyclist-friendly infrastructure.
