Alaskan Way Viaduct Replacement Program.

This map shows the projects that will replace SR 99 through Seattle

Click this map to see related projects

Click on the project boxes for more information. Click the X in the corner to close this window

Building a new State Route 99 through Seattle

In summer 2013, the world’s largest-diameter tunneling machine began a historic journey beneath downtown Seattle. Its purpose: dig a tunnel to replace the SR 99 Alaskan Way Viaduct, a double-deck highway that has spanned the downtown waterfront for more than 60 years.

The machine’s task sounds straightforward enough, but the story behind it is complicated. It begins with an earthquake in 2001 that damaged the viaduct and led to a decade of debate about how to replace the structure. The story's conclusion is unfolding now, as we at the Washington State Department of Transportation, along with our agency partners, build a new SR 99 corridor through Seattle that includes:

  • 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.


The tunnel will change the way traffic uses SR 99 in Seattle. Drivers approaching the tunnel from either direction will face a choice depending on their destination: use the tunnel to bypass downtown or exit to city streets and head into downtown. At the tunnel’s north end, downtown access will be similar to today, with on- and off-ramps near Seattle Center. From the south, new on- and off-ramps will connect SR 99 to downtown via the new waterfront street.

Halfway there

Half of the viaduct is already gone, demolished and replaced by our crews at the south end of downtown, near Seattle’s stadiums. Completed on budget and one year ahead of schedule, this new section of SR 99 connects to the remaining viaduct along the waterfront to keep SR 99 traffic moving until the tunnel opens to traffic.

Related projects

As part of the Alaskan Way Viaduct Replacement Program, King County, City of Seattle and the Port of Seattle are planning street, transit and waterfront improvements. Click on the related projects map above to learn more.

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, helps attract visitors and business to Pioneer Square. WSDOT’s parking mitigation program focuses on strategies that offset construction-related on-street parking impacts in Pioneer Square and the waterfront neighborhoods.