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SEATTLE — The Washington State Department of Transportation (WSDOT) signed a contract with Seattle Tunnel Partners to design and build the SR 99 bored tunnel — the preferred alternative for replacing the seismically unsafe Alaskan Way Viaduct along Seattle’s downtown waterfront.

In a ceremony held at the Port of Seattle, Washington State Transportation Secretary Paula Hammond signed the design-build contract with Seattle Tunnel Partners representatives Fernando González Alcañiz and Jack Frost.

“With this contract, we are confident that the tunnel will be built within budget and delivered on time,” Washington Transportation Secretary Paula Hammond said. “More than 90 percent of the design-build work will be performed for a fixed price.”

In addition to Seattle Tunnel Partners’ proposal price of just under $1.09 billion, the contract includes allowances for inflation, bonding, and insurance requirements. Utility work reimbursed by the city of Seattle also is included in the contract. This brings the total contract amount to $1.35 billion, with as much as $70 million in incentives.

WSDOT will direct the design-build team to continue preliminary design work in February. If tunnel plans are approved at the conclusion of the project’s environmental review, expected this summer, the agency will direct the design-build team to begin final design and construction of the bored tunnel.

The Federal Highway Administration, WSDOT, and the city of Seattle have identified a two-level, 1.7-mile tunnel from S. King Street to Thomas Street as the preferred replacement for the central section of the vulnerable double-deck viaduct. WSDOT’s review of the tunnel and other alternatives for replacing the viaduct began in 2001.

WSDOT named Seattle Tunnel Partners the apparent best-value bidder in December 2010 based on a combination of bid price and technical score for their project proposal. The team exceeded WSDOT requirements by proposing to build a tunnel that includes an 8-foot-wide safety shoulder in each direction of traffic. The contractor team also proposes to open the tunnel to traffic by late 2015 — a year sooner than WSDOT required.

The design-build contract requires Seattle Tunnel Partners to take a greater share of the risk than a traditional construction contract. WSDOT will manage the project to ensure it is completed on time and on budget by consulting with a panel of international tunnel experts, utilizing an innovative dispute resolution process, and implementing a risk management plan.

Seattle Tunnel Partners, a joint venture of Dragados USA and Tutor Perini Corp., is one of two teams that competed for the SR 99 bored tunnel design-build contract. Key members of the team delivered the comparable 49.5-foot-diameter Madrid M-30 highway tunnel in Spain. The team includes several local firms, including Frank Coluccio Construction, Mowat Construction, and HNTB Corp.

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.

Total cost of the proposed bored tunnel is estimated to be $1.96 billion. This includes design, right-of-way acquisition, construction management, and more than $200 million set aside for risk. Also included in the $1.96 billion are separate, future construction contracts for roadway connections at the north and south ends of the tunnel.

For more information on the Alaskan Way Viaduct and Seawall Replacement program, visit www.alaskanwayviaduct.org.