This map shows the projects that collectively replace SR 99's old route through Seattle.

Building a new State Route 99 through Seattle

The Alaskan Way Viaduct, an elevated section of State Route 99 in Seattle, was built in the 1950s, and decades of daily wear and tear took a toll on the structure. Because of the viaduct’s age and vulnerability to earthquakes, replacing it was critical to public safety.
The Alaskan Way Viaduct Replacement Program includes projects led by the Washington State Department of Transportation, King County, the City of Seattle and the Port of Seattle. The Federal Highway Administration is a partner in this effort. 

Major elements of the program include:

  • A two-mile-long tunnel beneath downtown Seattle.
  • A mile-long stretch of new highway that connects to the south entrance of the tunnel, near Seattle’s stadiums.
  • A new overpass at the south end of downtown that allows traffic to bypass train blockages near Seattle’s busiest port terminal.
  • Demolition of the viaduct’s downtown waterfront section.
  • A new Alaskan Way surface street along the waterfront that connects SR 99 to downtown.

Our schedule page includes a list of all 30 projects that are led or funded by the state as part of this effort.

Related projects

As part of the Alaskan Way Viaduct Replacement Program, our partner agencies are planning street, transit and waterfront improvements.

Changing access

The SR 99 tunnel changes the way traffic uses SR 99 in Seattle. Drivers approaching the tunnel from either direction face a choice depending on their destination: use the tunnel to bypass downtown, or exit SR 99 to reach city streets and head into downtown. The SR 99 tunnel opened on Feb. 4, 2019. Visit 99tunnel.com for more information on how to use the tunnel.

Construction mitigation

We work closely with residents and businesses near the viaduct to help them through construction. Milepost 31, our award-winning project information center, helped attract visitors and business to Pioneer Square for six years during project construction. WSDOT’s parking mitigation program focuses on strategies that offset construction-related on-street parking impacts in Pioneer Square and the waterfront neighborhoods.

Agency Partners

The Alaskan Way Viaduct Replacement Program is a partnership between the following public agencies:

The Federal Highway Administration (FHWA) is responsible for ensuring that the viaduct replacement projects meet federal regulations.

The Washington State Department of Transportation (WSDOT) owns SR 99. The agency is responsible for highway inspections and major maintenance, and for ensuring that state regulations are followed. 

King County is responsible for implementing transit changes and improvements associated with the program.

The Port of Seattle relies heavily on the SR 99 corridor and has committed $300 million in funding to the program.

The City of Seattle is responsible for surface street traffic operations and minor maintenance. In addition, the city owns and maintains Alaskan Way, the area underneath the viaduct, and many of the utilities located in the project area.

US Department of Transportation - Federal Highway Administration. Washington State Department of Transportation. King County Port of Seattle. The City of Seattle.