While federal inspectors have called the collapse ‘structural in nature' (as opposed to an act of terrorism), the exact cause is yet to be identified.
"With the cause of the collapse unknown, the federal Transportation Department said it had told all states to inspect bridges similar to the steel-deck truss span that fell "or, at minimum, review inspection reports to determine if further action is needed." The department said there were 756 such bridges.
The bridge here was deemed "structurally deficient" in 1990, state engineers said, in part because of some corroded bearings, but it was not expected to be replaced until 2020.
Dan Dorgan, a state bridge engineer for the Minnesota Department of Transportation, said a "deficient" designation did not mean a bridge needed to be immediately replaced; 77,000 bridges across the country, he said, have a similar designation."
"National Transportation Safety Board officials arrived to begin an investigation into why the eight-lane bridge, which opened in 1967 and became a staple for most Minneapolis commuters, had in a matter of seconds fallen 60 feet in a cloud of dust.
Among the evidence the safety board must now consider, said Mark Rosenker, its chairman: footage of the collapse captured by a security camera, a computer analysis of the failure and decades of the bridge's inspection reports."
"Minnesota Governor Pawlenty promised a thorough investigation of what went wrong and said the state would hire an outside firm to conduct it, even as the federal safety board began conducting its own. He also announced immediate inspections of the state's three other bridges that mimic the design of the 35W bridge.
Mr. Pawlenty said the issue of old, crumbling bridges and roads, however, stretched far beyond Minnesota's borders. "This is a national problem," he said.
[Ed' note: See related links for California and New York bridges].
"Many of the nation's highways and bridges are as old as the bridge here or older, and in recent months leaders in Congress have been debating how to pay for so many needed improvements.
Mary E. Peters, the secretary of Transportation, traveled to the scene of the disaster. Ms. Peters said Minnesota's transportation officials seemed to have done "everything appropriate" in their monitoring of the bridge.
"But clearly we need to understand what happened here," she said. "Bridges in America should not fall down."