The Alaskan Way Viaduct has been an important part of Seattle’s highway infrastructure since it was completed in 1953. This double-decker elevated highway is part of State Route 99, skirting along the downtown area of Seattle along the Elliott Bay waterfront of the Puget Sound. The Viaduct carries up to 110,000 vehicles a day, but has long been due for an upgrade. This was made clear in 2001, when an earthquake damaged the motorway.
Seismic experts had already been considering a project to strengthen the highway, but this earthquake made the need for reinforcement more urgent. However, the project has been the source of heated political debate for the past decade. It was eventually determined that replacing the viaduct would be easier and cheaper than repairing it. Another issue with the viaduct is that the elevated roadway cuts off downtown Seattle from the waterfront. A replacement tunnel was finally agreed upon as a solution to both problems. The tunnel was approved by a voter referendum in 2011, allowing the project to move forward.
Boring of the new replacement tunnel began this year, with the viaduct to be rebuilt according to modern seismic standards. When all is said and done, the new tunnel and roadway should be able to withstand an earthquake up to a 9.0 magnitude. In the 2001 Nisqually earthquake, the Alaskan Way Seawall was damaged along with the viaduct, requiring $14.5 million to be spent on emergency repairs. When the 1989 Loma Prieta earthquake struck the Bay Area in California, the Cypress Street Viaduct in Oakland California was damaged in a similar way, causing 42 deaths. Seismic experts have been strong proponents of this project, in order to prevent a similar disaster.
The south half of the viaduct has already been demolished, with traffic rerouted onto a bridge located near Seattle’s sports stadiums instead. A new roadway will be completed in 2014, while the tunnel is slated to open up to traffic by the end of 2014. This new two-mile tunnel will carry State Route 99 underneath downtown Seattle, connecting it from the SoDo neighbourhood to South Lake Union in the northern part of the city. The massive tunnel will be able to accommodate all sizes of vehicles, from petite Holden cars to lightweight trucks en route to the Port. The tunnel will also maintain freight routes, most freight will be able to use the SR 99 tunnel, including car transporters.