A consultant for the state Transportation Department recommended installing high-tech sensors to detect cracking on critical sections of an interstate bridge less than a year before the span collapsed, killing 13 people, records show.The recommendation made in a November 2006 report was considered but the agency ultimately went with other kinds of inspections because there were no signs of cracking on bridge trusses, said Dan Dorgan, a state bridge engineer. "In the absence of cracks, we had no locations to monitor or information to orient monitors for crack detection," Dorgan wrote in response to written questions from The Associated Press.

The cause of the Aug. 1 collapse, which also injured about 100 people, is under investigation.



In the years leading up to the collapse, the state DOT and private consultants performed numerous evaluations and inspections of the bridge that raised concerns about its condition. The DOT contracted with URS Corp. in 2003 to perform a more thorough analysis of fatigue in the bridge support structure.

The AP reviewed nearly 13,000 pages of documents obtained under an open records request relating to the URS Corp. contract.

The company indicated in its study of the bridge between 2004 and 2006 that there were 20 fracture critical truss beams on the bridge — those considered to be "the most susceptible locations for crack initiations."

The URS study recommended an acoustic emission monitoring system that included the capability of alerting the state DOT immediately about specific locations on the bridge "where unusual signals are detected indicating the possibility of steel cracking."

Mark Carlos, president of Physical Acoustics Corporation, which makes such monitors, said there's no way to know whether such monitors would have detected the impending bridge collapse.

Acoustic emission monitoring differs from the way bridges are typically inspected; it detects cracks while they are occurring, instead of trying to spot them after they've happened, Carlos said.

The cost of installing the monitors in a specific area of a bridge, as was proposed by URS, would cost between $20,000 to $40,000, Carlos said. The devices are used on some bridges around the country but are not yet common, he said.

Dorgan said that DOT inspectors instead utilized ultrasonic testing, which he called a "proven means of actually detecting cracks."

Ron Low, a spokesman for URS, said that the company would not comment on any of the findings or recommendations related to its inspections of the bridge.

Two Minnesotans sued the state Transportation Department Tuesday, claiming its $234 million contract with Flatiron Constructors of Longmont, Colo., is illegal and harms taxpayers. Flatiron's bid was the most expensive and tied for the longest amount of time, but the company beat three other teams on a technical score that accounted for factors such as quality and aesthetics.

In their lawsuit filed in Ramsey County District Court, the plaintiffs seek to void the contract.

DOT spokeswoman Lucy Kender said it would be inappropriate for anyone at the agency to discuss a pending lawsuit.

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Associated Press writers Elizabeth Dunbar in Minneapolis and Martiga Lohn in St. Paul contributed to this report.