Last month, construction crews placed a series of hollow tubes over the Wanzer Brook in Fairfield as part of a Vermont Transportation Agency program that uses new technology to cut construction time, save money and reduce the backlog of bridges that need replacement.
The tubes, made of material that is impervious to the elements, have since been filled with concrete and construction crews are laying a deck across the top. The bridge, just under 35 feet long, should be ready for traffic within a few weeks, a fraction of the time it would take to build a traditional bridge.
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And by agreeing to close the road during construction, the town is paying about $45,000 on the $900,000 project, said Fairfield Town Clerk Amanda Forbes.
"They were really impressed with it," Forbes said of the town selectboard after it heard a proposal for the bridge.
The span, nicknamed a "bridge in a backpack," is an example of the innovative ideas that are part of Vermont's accelerated bridge program that uses quick-building designs and other innovations, such as closing the road to traffic during construction rather than building a temporary bridge, to save time and money.
The Fairfield bridge was developed at the University of Maine Advanced Structures and Composites Center. A handful of others have been built in Maine and New Hampshire, two in Michigan, and one in Trinidad.
Bridges can be built in weeks instead of months and there's no need for trucks to bring in heavy steel beams. The composite shell provides a protective barrier that keeps out road salt, chemicals and moisture, which eventually penetrate and degrade conventional bridges.
Tim Kenerson is a design engineer with Advanced Infrastructure Technologies, of Orono, Maine, which spun off from the university center. He said the first bridge was installed in 2008 and hasn't required any maintenance.
"If you think of it, there's really nothing in our system that can corrode or degrade," Kenerson said.
The idea behind Vermont's accelerated bridge program goes back several years, but the need for innovation was driven by Tropical Storm Irene when Vermont engineers were faced with the immediate need to repair or replace scores of bridges.
"We did it so much in Irene, it transformed our willingness to do it far more," said Vermont Deputy Transportation Secretary Sue Minter. "I think it's advanced us significantly and really helped us create this whole new program."
Several years ago, more than 30 percent of Vermont bridges were considered structurally deficient. That number is now under 8 percent, Minter said.
Wayne Symonds, the structures program manager for the Agency of Transportation, said most steel bridges last about 75 years with routine maintenance while the new technology is expected to last at least 100 years and require little maintenance.