Quality of Life Benefits of Transportation,  Safety,  Washington

Alaskan Way Viaduct Replacement Program

When it came to replacing Seattle’s seismically vulnerable Alaskan Way Viaduct with a deep-bored tunnel, The Washington State Department of Transportation had four guiding principles: Improve public safety, provide efficient movement of people and goods now and in the future; maintain or improve downtown Seattle, regional, port and state economies; enhance Seattle’s waterfront, downtown, and adjacent neighborhoods as a place for people.

WSDOT accomplished all this when the State Route 99 tunnel opened and the Alaskan Way Viaduct in Seattle was demolished.

The elevated Alaskan Way Viaduct carried SR99 through Seattle since the 1950s was a critical link for passenger and freight.

In 2001, a magnitude 6.8 earthquake damaged the viaduct. Concrete cracked and columns shifted as much as 5 inches. Repairs kept the road functioning, but removing the viaduct became a critical public safety issue.

Washington chose to build the world’s largest-diameter, machine-bored tunnel underneath Seattle’s downtown. Inside, stacked 32-foot roadways would carry SR 99. Public safety guided every design decision. Building a tunnel underneath the city to replace a viaduct above promised monumental improvement of Seattle’s waterfront and downtown. Partners and community members all joined with WSDOT for more than 20 years to advise, consult and ultimately decide how this massive project would make Seattle a better city. 

In February 2019, the two-mile-long tunnel opened, and WSDOT demolished the Alaskan Way Viaduct. Drivers now use the tunnel every day for safe, fast trips underneath downtown Seattle. They use a tunnel designed to withstand powerful earthquakes and designed for safety with state-of-the-art fire suppression, ventilation, traffic and security systems. 

The success of this tunnel opened up a new world of possibilities for cities considering alternative tunneling solutions.

And Seattle is building a multi-modal thoroughfare and a promenade along its waterfront with new public space for all.


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