Tunnelling the Alaskan Way

In the United States, the Washington State Department of Transportation has announced that it has chosen a 1.8km long tunnel as the preferred option to replace the Alaskan Way Viaduct in Seattle.

The viaduct requires replacement as it and the adjoining seawall are deemed to be at risk of failure from earthquakes. The tunnel will cost roughly US$1bn more than the other alternatives considered, but it has the advantage of allowing the waterfront district of the city to be opened up more for business and development.

Costed at between US$3.4 to 4.1bn, the tunnel would take seven to nine years to complete. The recent decision does not guarantee the tunnel will be built however as funding and a detailed environmental impact report have yet to be addressed. For this reason, a contingency plan of rebuilding the existing viaduct is also being studied.