The Alaskan Way Viaduct, completed on April 4, 1953, is a double-decked elevated section of State Route 99 that runs along the Elliott Bay waterfront in Seattle's Industrial District and downtown Seattle. It is the smaller of the two major north–south traffic corridors through Seattle (the other being Interstate 5), carrying up to 110,000 vehicles per day. The viaduct runs above the surface street, Alaskan Way, from S. Nevada Street in the south to the entrance of Belltown's Battery Street Tunnel in the north, following previously existing railroad lines.

The viaduct was damaged in the 2001 Nisqually earthquake, and is proposed to be replaced by an underground tunnel.

Earthquake concerns

The 1989 Loma Prieta earthquake destroyed the similarly designed Cypress Street Viaduct in Oakland, California with considerable loss of life. The 2001 Nisqually earthquake damaged the viaduct and its supporting Alaskan Way Seawall and required the Washington State Department of Transportation (WSDOT) to invest US$14.5 million in emergency repairs. Experts give a 1-in-20 chance that the viaduct could be shut down by an earthquake within the next decade. Since the Nisqually Earthquake occurred, semi-annual inspections have discovered continuing settlement damage.

Due to damage from continuing settlement, a group of researchers and faculty from the University of Washington urged the mayor of Seattle (in 2007) to close the viaduct within a four-year timeframe.

Proposed replacement

On January 12, 2009, the state of Washington, King County, the city of Seattle, and the Port of Seattle revealed that they had agreed to replace the viaduct with a four-lane, 2-mile (3.2 km) long underground tunnel. The tunnel would have a south portal in SoDo, near Qwest Field, and a north portal near Thomas Street, north of the Battery Street Tunnel.

The project is estimated to cost US$4.25 billion, with the state, city, and county promising funding well short of the estimate. The state will fund boring of the tunnels, while the city and county will fund surface street improvements and repairs to the Alaskan Way Seawall, which itself was damaged in the Nisqually earthquake. There is at present no publicly-known timetable for the construction and opening of the tunnel. Construction of the tunnel is scheduled to begin in early 2011 and end in late 2015, with the potential length of the project being 6 years.

The announcement did little to quell the long and heated debate over the viaduct's replacement, with several factions expressing their criticism over the tunnel decision.

Route description

Heading northbound on State Route 99, the viaduct begins about a mile north of the First Avenue South Bridge, passing over the west end of the Industrial District. Just south of Safeco Field, at Massachusetts Street, the bridge shifts from a side-by-side alignment to the double-deck alignment commonly associated with the Alaskan Way Viaduct, with northbound traffic on the upper deck and southbound traffic on the lower deck. Then, at approximately Pike Street, the bridge reverts to a side-by-side alignment for about ½ mile until the viaduct's north end at the entrance to the Battery Street Tunnel.

Entrances and exits

Building Activity

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