State highway officials named the presumptive team to construct a deep-bore tunnel today, Seattle Tunneling Partners (STP), which submitted the most expensive bid but nearly doubled its competitor in technical credits. The proposal, coming in a hair under the state's $1.09 billion limit, would result in a wider tunnel than the state previously expected to replace the Alaskan Way Viaduct.

Already proposed as widest deep-bore tunnel ever constructed at 56 feet in diameter, STP’s design merited more technical credits, first, because it added two additional feet to shoulders in the tunnel roadway. That would widen the tunnel's shell to “approaching 58 feet,” Alaskan Way Viaduct Replacement Project director Ron Paananen said. The wider shoulders address some concerns that there wasn’t enough room for a car to pull over inside the tunnel.

But a wider tunnel may increase risk. A consultant hired by the city this summer, Thom Neff, cautioned that coming in on budget was "unlikely" because the width was unprecedented at 56 feet in diameter. Another set of city consultants predicted the project has a 40 percent chance of running over budget.

Governor Chris Gregoire cheered the bids and as evidence that the tunnel would be produced without cost overruns, which a state law says will be collected from Seattle property owners. "We are going to stay by our commitment," she said. "We are going to be on time. We are going to be on budget."

Meanwhile to its credit, STP’s proposal would narrow the roadway at the southern portal by two or three lanes (previous designs show it as wide as 14 lanes) and submerge the tunnel further south (which could allow technical challenges to be solved before the boring machine passes underneath unstable buildings and soil in Pioneer Square to the north). Lastly, STP said it could finish the project three months earlier.

More after the jump.

Details on the design proposals cannot yet be released, Paananen said. Both teams are entitled to a nine-day period to challenge the technical ratings. The losing team, Seattle Tunneling Group, is expected by many people to challenge the final score.

Gregoire also gave a nod to a state study that shows the tunnel will accommodate about one-third of the existing viaduct traffic, while the rest would choke downtown streets and I-5. That traffic would be worse without the tunnel, she argues, saying, “We will move cars through the tunnel and we will not displace them.”

Seattle Tunnel Partners is a joint venture of Dragados USA and Tutor Perini Corp, including Frank Coluccio Construction, Mowat Construction, HNTB Corp. and Intecsa. Seattle Tunneling Partners earned 71,577,000 technical points and a bid of $1,089,702,000. In contrast, Seattle Tunneling Group won only 38,152,000 points and submitted a bid of $1,088,202,000.