The Washington State Department of Transportation (WSDOT) has awarded a US$ 1.35 billion contract for the construction of a tunnel replacement to the Alaskan Way viaduct in Seattle to Seattle Tunnel Partners, a joint venture of Dragados and Tutor Perini.

Dragados is a subsidiary of Spanish contractor ACS.

The SR 99 bored tunnel is planned to replace the seismically unsafe Alaskan Way Viaduct along Seattle's downtown waterfront.

The contract involves designing and building the alternative route in the form of a two-level, 2.7 km stretch of tunnel from King Street in the south of the city to Thomas Street in the north, replacing the vulnerable coastal highway.

Seattle Tunnel Partners will be responsible for tunnel boring, mitigation for tunnel settlement, construction of tunnel portals, building the road within the tunnel and constructing two operations buildings.

The WSDOT said Seattle Tunnel Partners had proposed a price for the project of around US$ 1.09 billion. The total contract amount of US$ 1.35 billion includes up to US$ 70 million in incentives as well as allowances for inflation, bonding, insurance requirements and utility work.

WSDOT estimated the total cost of the project to be US$ 1.96 billion - a figure which includes right-of-way acquisition and separate, future construction contracts for road connections at the north and south ends of the tunnel.

The Seattle Tunnel Partners contractors plan to open the tunnel to traffic by late 2015 - a year sooner than WSDOT required. Preliminary design work on the project begins in February.

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