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SR 99 Bored Tunnel Video - October 2010Seattle—Starting Oct. 21, Seattle’s Alaskan Way Viaduct—an integral segment of SR-99, one of Seattle’s major north-south highways—will be demolished, making way for a new tunnel that will be safer in the event of an earthquake.
The aging viaduct, which accommodates 100,000 vehicles daily as well as trucks transporting goods to and from the Port of Seattle, is at risk in the event of an earthquake. The risk is due to a weakened structure and a deteriorating seawall that holds fill soil in place.
In its current condition the the Alaskan Way Viaduct could face a similar fate to the Cypress Street Viaduct in Oakland, Calif., which collapsed in the 1989 Loma Prieta Earthquake. Approximately 41 lives were lost in that event according to the U. S. Geological Survey’s website.
In the mid-1990s, due to several large earthquakes around the world, the Washington State Department of Transportation (WSDOT), began exploring options to replace the Alaskan Way Viaduct. The 2001 Nisqually earthquake in Seattle, which caused additional damage to the foundation of the viaduct, made the need for a seismically sound replacement more urgent. The solution WSDOT opted for was to demolish the viaduct and bore a tunnel underneath downtown Seattle.
“There were about 100 options that were boiled down to three; you have to do a lot of homework before you make this kind of decision,” said Travis Phelps communications staff for the WSDOT in a phone interview.
But given the present state economy, with Washington state forecasting a $1.4 billion revenue deficit, funding for the project is challenging. With the tunnel project total cost estimated at $3.1 billion, $2.4 billion will come from the state gas tax and federal sources, $700 million from tolls on the tunnel, and $300 million from the Port of Seattle, according to the WSDOT.
According to WSDOT, the new tunnel will be able to withstand an earthquake in the range of 9.0 on the Richter scale without collapsing. As the region continues to grow the tunnel will also improve mobility through downtown Seattle, a much-needed anecdote to the congested traffic the city is infamous for.
The estimated completion date and opening of the SR-99 tunnel is late 2015.
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