The State Thruway Authority gave final approval Monday to a plan to build a new Tappan Zee Bridge for $3.1 billion.

The authority's board voted 7-0 to award the bridge contract to the low bidder, a consortium of companies known as Tappan Zee Constructors. The consortium is led by Fluor Enterprises of Irving, Texas, and American Bridge of Coraopolis, Pa.

With the vote, Gov. Andrew Cuomo's administration has cleared another key hurdle in its efforts to break ground by early 2013 on a project that now ranks as the nation's most ambitious pending capital works project.

The plan calls for a dual-span bridge to be built in approximately the same location as the existing span, with construction expected to take more than five years.

"This is truly a historic day for the New York State Thruway Authority," said board chairman Howard Milstein in casting his vote.

"This is a major milestone for a bridge project that was a metaphor for the dysfunction of government and is now a national model for progress," Cuomo said.

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The committee's decision was not surprising. Two weeks ago, a panel of architects, designers and financiers handpicked by Cuomo said it favored the consortium's $3.1 billion bid as the one that represented the "best value." The final price could climb an additional $800 million when all costs are factored in, state officials have said.

The winning bid came in nearly $1 billion less than competitors' bids of $3.9 billion and $4 billion, respectively. It was some $2 billion less than the Cuomo administration's own original estimates.

Larry Schwartz, secretary to the governor, signaled the administration's preference for the consortium's bid in advance, emphasizing its low cost as well as a dredging plan that will have less impact on the Hudson River's aquatic environment. Early Monday, Thruway Authority Director Tom Madison said he favored the low bid as well.

Tappan Zee Constructors' plan calls for some 600,000 cubic yards less of dredging than the next-closest bid.

Dredging has been a concern at Riverkeeper, one of the Hudson Valley's leading environmental groups. Riverkeeper is still weighing a possible legal challenge to the bridge. The group has said it wants to see more detail on the final plans before deciding whether to pursue litigation that could put the project on hold.

Fluor and American Bridge are partners in the consortium with two other companies, Granite Construction Northeast, the California-based company that rebuilt the foundations of the World Trade Center and the memorial there, and Traylor Bros. Inc., based in Indiana.

"The combined experience of our team enabled us to put forward an attractive and cost competitive design," said Steve Dobbs, president of Fluor's Industrial & Infrastructure Group.

Dobbs said Fluor's design reduced the weight of the bridge structure and reduced the number of foundation structures that will be needed. The design minimizes the number of piers and give the bridge a sleeker look, Dobbs said.

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Fluor and American Bridge teamed up to build a replacement for the earthquake-damaged Bay Bridge in San Francisco -- a project that held together through more than a decade of political wrangling and setbacks. Fluor officials said Monday they will be using a crane specially designed for the Bay Bridge project on the Tappan Zee bridge.

Slated for completion in 2013, the new Bay Bridge was first proposed in 1989, after the original bridge was damaged in an earthquake. During the 24 years between conception and completion, the cost of the new bridge ballooned from $1 billion to nearly $7 billion. Steelworker unions protested the decision to use prefabricated Chinese steel in the new bridge, and the cost overruns caused political fallout.

"Our governor, Gray Davis, was pretty much recalled because of the mess of the Bay Bridge," said Abolhassan Astaneh-Asl, an engineering professor at the University of California at Berkeley.

Cuomo aides have vowed to avoid such pitfalls.

This summer, they announced a labor agreement with 14 major trade unions. The agreement will ensure that the project isn't stalled by work shutdowns that could cost as much as $1 million per day. Equally important, the contract with the winning consortium will be a "design build" contract that requires builders to cover most unforeseen costs.

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Cuomo has promised that only U.S.-made steel will be used on the Tappan Zee.

"I don't see anything you could say they could do better," Astaneh-Asl said of the state's plans for the new Tappan Zee Bridge. "It looks to me like they've done their homework."

The Bay Bridge project mirrors the Tappan Zee plan in many ways, Astaneh-Asl said.

Both bridges span busy waterways. In both areas, environmentalists are passionately committed. Both designs entail twin roadways. Both have long sections of traditional elevated highways on either side of the central bridge spans.

But there are also important differences between the two projects. The new Bay Bridge is a so-called self-anchored suspension bridge -- the biggest such bridge in the world -- with main suspension cables anchored to the deck of the bridge itself, rather than to massive concrete and steel structures at either end of the bridge.

The self-anchored approach is relatively innovative in bridge-building circles -- having been used in fewer than a dozen major bridges over the past 60 years -- in part because it is considered more difficult to execute than more traditional approaches. To casual observers, the approach looks a lot like traditional suspension bridges such as the George Washington Bridge. The only major difference is the presence of the massive anchorage towers at either end of the George Washington Bridge.

On the other hand, the winning design for the new Tappan Zee is a "cable-stayed" approach. Such a bridge is supported by many individual cables that are connected at one end to the bridge deck and at the other to central towers. There are no anchorages, no main cables hanging between the towers and no suspender cables connecting the main cables to the deck.

The cable-stayed approach is unfamiliar in the United States, having been used in relatively few projects here, but has been heavily used and proven practical in scores of projects in Asia and South America in past decades.

"I'm very glad they didn't go with self-anchored," Astaneh-Asl said. "In bridge engineering, you don't do innovation. You do evolution. You spend $3 billion, you want to make sure it's safe and sound and lasts 100 years. You don't experiment."

With a winning bid in hand, the Cuomo administration can now focus fully on its financing plan, including how high tolls will need to be raised to pay for the bridge in the long term.

Transportation analysts say the low cost of the winning bid could translate into a less costly toll hike, possibly knocking as much as $5 off the $14 bridge toll Cuomo administration officials once forecast. Cuomo since has backed off the $14 projection.

On Monday, Thruway Authority Board Chairman Howard Milstein said the cost savings could knock between $5 and $7 off future tolls.

The state is seeking a low-interest loan from the U.S. Department of Transportation to cover half the cost of the project. The rest would be paid for with the sale of Thruway Authority-backed bonds. Both would be paid back with money raised from tolls.

The planned bridge will be transit-ready, meaning that rail service can be added to the bridge in the future. Cuomo said adding a mass transit feature now would more than double the cost of the project.

Two weeks ago he named a mass transit task force to explore transit options. Among its members is Westchester County Executive Rob Astorino, who initially withheld his support for the bridge while expressing concern about the plan's lack of a transit option.

The bridge will include a dedicated rush-hour bus lane.

"After so many years of gridlock, building a safer and less congested bridge as soon as possible is the most attractive option for Westchester," Astorino said.