Project Purpose and Need
The purposes of the I-5/SR 509 Project areto improve regional highway connections by extending SR 509 to serve future transportation needs in southwest King County and to enhance southern access to Seattle-Tacoma International Airport.
Existing travel corridors such as Interstate 5 (I-5) and State Route (SR) 99 are now highly congested during the peak hours of travel. By the year 2020, traffic volumes are expected to increase by at least 35 percent due to population growth, economic expansion, and increased airport activity. This increase will cause existing transportation facilities to operate in a stop-and-go condition, with associated long delays. Extending SR 509 to a junction with I-5 would mean a more efficient use of the existing SR 509 for serving downtown Seattle, the Port of Seattle, and south King County industrial areas and would relieve traffic on existing arterials by shifting through traffic to the new roadway. SR 509 would also provide a route for new transit service and high occupancy vehicle (HOV) lanes. Airport traffic to and from the south would be diverted from the congested SR 99 and South 188th Street corridors to an improved access to Sea-Tac Airport.
Project Description
Construction for the initial phase of the SR-509/I-5 Freight Corridor Completion and Freight Improvement Project will include:
- a new two-lane road between South 210th Street and 24th/28th Avenue South in SeaTac for a new southern airport access
- a new four-lane road between 28th Avenue South and South188th Street in SeaTac and Burien
- a new SR 509 interchange at 28th Avenue S
- collector/distributor lanes to I-5 from South 210th Street to SR 516.
- a rebuillt the I-5/SR 516 interchange, including a new connection to South S. 231st Way
- new lanes added to I-5 from the SR 516 interchange to S. 320th street interchange
Future phases will provide additional lanes between South 188th Street and 24th/28th Avenue South, HOV lanes on SR 509, SR 509 HOV direct connection to I-5 HOV, a new South Access Road, grade separation of the airport south access road and S. 200th St., and new connections to S. 200th St. from SR 509.
Background
In 1992, growing concern over the increasing congestion in the Interstate 5 and SR 99 corridors in the cities of SeaTac and Des Moines and access to Sea-Tac International Airport led to a cooperative effort to develop a regional solution. This effort, a multi-jurisdictional endeavor to find transportation solutions meeting the needs of the area, is being undertaken by the affected cities and agencies. The project Executive Committee, consisting of elected officials and agency executive management, is the decision making body for the project. Ongoing guidance on technical and process direction is provided by a Steering Committee, comprised of senior professionals representing each agency, the Federal Highways Administration, the Federal Aviation Administration, and the public.
In 2011 WSDOT applied for and received a grant from the Transportation Research (TRB) Strategic Highway Research Program 2 (SHRP2) to pilot test a collaborative decision making process. That process, now complete, was to find a mutually acceptable first phase for the project that could be partially funded by tolling the project. The adopted first phase is described above.
Project Benefits
Statewide Benefits
- Improves freight mobility within the entire South King County area. This is the heaviest traveled freight corridor in the Pacific Northwest and is important to the state's economic growth. Will also improve air freight mobility to Sea-Tac Airport.
- Completes one of two last unfinished state freeway segments in the region. Currently, SR 509 represents an underutilized public investment.
- Provides a direct south access link between Interstate 5 and the state's hub airport.
Regional Benefits
- Improves traffic flow on I-5 from S 320th St to Seattle.
- Links Seattle via SR 509 and the new First Avenue South Bridge with the south King County region.
- Provides a direct freight corridor from the industrial area of Seattle to Tacoma and the Kent area.
- Makes long-term improvements to the SR 516 interchange.
- Diverts traffic from the heavily congested Southcenter Hill and adds lane capacity to I-5 as far south as South 320th Street in Federal Way, all of which will benefit I-5 from proposed expansion of I-405.
- Provides for future HOV access between South Seattle and South King County.
- Allows convenient access to the southern terminus of the proposed Sound Transit Light Rail station at South 200th Street, and provides a direct route from Interstate 5 to the airport for Sound Transit's Tacoma Region Express Bus route.
Local Benefits
- Allows the city of SeaTac to become an "urban center" and accommodates development in Des Moines. Allows access to a large amount of industrially zoned land in the vicinity of the airport.
- Reduces congestion and air pollution on neighborhood streets in SeaTac, Burien, Des Moines, Federal Way, and Normandy Park.
- Designed to be environmentally sensitive and will improve the habitat and water quality in the effected drainage basins.