State Route 518

State Route 518
State	WA
Type	SR
Route	518
Length mi	3.42
Established	1964
Direction a	West
Terminus a	Interstate 5 in Tukwila, Washington
Direction b	East
Terminus b	Interstate 405 in Bellevue, Washington
Counties	King County, Washington

State Route 518 is a short controlled-access highway in King County, Washington connecting Interstate 5 near Tukwila, Washington with Interstate 405 near Bellevue, Washington. The route provides a crucial link between the Seattle–Tacoma International Airport area, the Port of Seattle, and the eastern suburbs including Renton, Washington and Kirkland, Washington. It forms part of the regional freight and commuter network linking Seattle, Washington with southeastern King County, Washington corridors and interfaces with major arterials such as State Route 167 and State Route 99.

Route description

SR 518 begins at a junction with Interstate 5 adjacent to the Westfield Southcenter Mall and proceeds southeast as a freeway serving the Seattle–Tacoma International Airport access roads and the Port of Seattle facilities. The highway crosses urban industrial districts associated with the Tukwila City Council planning area and intersects ramps to State Route 99 and airport terminals used by carriers such as Alaska Airlines and Delta Air Lines. Continuing east, SR 518 skirts the northern edge of Renton, Washington and provides connections to surface streets controlled by King County, Washington and the Washington State Department of Transportation before meeting Interstate 405 near Bellevue, Washington and the South Bellevue Park & Ride serving Sound Transit bus routes and King County Metro.

The corridor passes through areas impacted by transportation projects led by agencies including the Puget Sound Regional Council and the Federal Highway Administration, and it carries a mix of commuter, airport, and freight traffic linked to the Port of Tacoma and inland distribution centers. Adjacent land uses include commercial centers influenced by developers tied to projects like the Southcenter Mall expansion and corporate campuses anchored by firms such as Boeing and local technology companies in the Seattle metropolitan area.

History

The SR 518 alignment traces its origins to early 20th-century highways serving Seattle–Tacoma International Airport development and the growth of Tukwila, Washington as an industrial hub. Original planning involved coordination with the Washington State Legislature and the State Highway Commission in mid-century efforts to modernize state routes for increasing automobile ownership associated with national trends after World War II and the interstate program championed during the administration of President Dwight D. Eisenhower.

Designated during the 1964 statewide highway renumbering overseen by the Washington State Highway Commission, SR 518 was constructed and upgraded in stages to full freeway standards to accommodate traffic between I-5 and I-405. Major improvements occurred in response to regional growth driven by employers including Microsoft and Amazon (company) in the late 20th and early 21st centuries, as well as airport expansions carried out by the Port of Seattle and the Federal Aviation Administration. Environmental reviews and permits involved agencies such as the Washington State Department of Ecology and local jurisdictions like the City of Tukwila.

Accidents and congestion in peak travel periods prompted safety and capacity upgrades, with investments funded through state transportation budgets approved by members of the Washington State Legislature and local ballot measures endorsed by entities like the Sound Transit Board.

Major intersections

- Western terminus: junction with Interstate 5 near Tukwila, Washington and access to State Route 99 and Westfield Southcenter Mall. - Airport access: ramps serving Seattle–Tacoma International Airport facilities and employee parking tied to the Port of Seattle. - Local connections: interchanges providing access to arterial streets in Tukwila, Washington and Renton, Washington under the jurisdiction of King County, Washington. - Eastern terminus: junction with Interstate 405 near Bellevue, Washington, with connecting ramps to I-90 toward Seattle, Washington and Issaquah, Washington.

Related routes

SR 518 interfaces with multiple state and interstate routes including Interstate 5, Interstate 405, State Route 99, and State Route 167, forming part of a network that serves freight providers such as the Port of Seattle and regional transit agencies such as Sound Transit and King County Metro. The corridor’s relationship with Interstate 90 via I-405 creates linkage to eastern suburbs like Issaquah, Washington and technology employment centers tied to Microsoft and regional offices of firms like Google, while connectivity to SR 99 supports access to downtown Seattle, Washington and legacy arterial corridors with historical ties to the Pacific Highway.

Future and improvements

Planned improvements to the corridor are coordinated by the Washington State Department of Transportation and regional planners at the Puget Sound Regional Council, with goals including safety enhancements, interchange reconfigurations, multimodal access for agencies such as Sound Transit, and freight movement optimization to support the Port of Seattle and inland distribution centers. Congestion mitigation strategies reference projects funded through state transportation packages enacted by the Washington State Legislature and proposals advanced by local governments including the City of Tukwila and City of Bellevue.

Proposals under consideration include ramp modifications to improve airport access used by carriers including Alaska Airlines, transit priority measures to benefit King County Metro and Sound Transit buses, and pavement rehabilitation to address wear from heavy truck traffic linked to logistics operators such as Amazon (company) and national carriers. Environmental permitting and community engagement processes involve the Washington State Department of Ecology and local stakeholders representing neighborhoods in Tukwila, Washington and Renton, Washington.

Category:Roads in King County, Washington