Immediately after the Minnesota bridge collapse, the Federal Highway Administration urged infrastructure managers to reinspect each of the nation's 756 steel arch truss bridges. Here, the Missouri DOT uses the Snooper bridge inspection truck, made by Omaha, Neb.-based Paxton-Mitchell Co., to check the conditions of the state's 11 such bridges. Photo: MoDOT
It was only 40 years old when it collapsed Aug. 1, but the I-35W Mississippi River Bridge in Minnesota had been deemed “structurally deficient” since 1997. Experts speculate the steel arch truss bridge collapsed because of weather extremes, vulnerable design, and/or metal fatigue.
The bridge had been retrofitted with the nation's first anti-icing system and other safety-enhancing technologies, and was scheduled for reconstruction in 2020. Although the University of Minnesota had concluded that the bridge's 52 trusses probably wouldn't crack, the Minnesota DOT (Mn/DOT) had San Francisco-based engineering design firm URS Corp. study the truss welds for potential cracking. When inspections earlier this year didn't find cracks, the agency postponed further inspections until after completion of scheduled paving work.
Charged with caring for 13,000 bridges, the department allocated maintenance funds to needier structures—a cost-benefit analysis familiar to all PUBLIC WORKS readers. Mn/DOT lost the gamble. Luckily, scheduled repairs had shut the bridge down from eight to four lanes, minimizing the number of deaths (13) on a bridge that otherwise carried 140,000 vehicles daily.
To date, MN/DOT stands to receive $250 million in federal emergency funds. On Oct. 8, it awarded a $234 million design-build contract to Flatiron-Manson, a joint venture of Flatiron Constructors Inc., Longmont, Colo., and Manson Construction Co., Seattle, as builder; and Figg Bridge Engineers Inc., Tallahassee, Fla., as designer, to rebuild the new 10-lane bridge with concrete. Other bidders learned the winning proposal was neither the lowest-cost nor fastest-completion, sparking national debate over the merits of design-build for public construction.
We've said it before, and we'll say it again: Emergency relief is an inefficient way to care for our infrastructure. Despite legislation introduced in both houses of Congress appropriating 20% more for bridge maintenance, the well will most likely remain dry.
It's doubtful the Bush administration will allow a gas-tax increase to boost funding for highway projects. And as popularity of hybrid vehicles rises, gas consumption may decline, taking revenues with it.
Meanwhile, transportation managers may be expected to scrutinize bridges even more closely. After a bridge connecting Ohio and West Virginia collapsed in 1967, killing 24, Congress established national bridge inspection standards, requiring inspections at least every other year.
Since then, federal response to bridge failures has been to intensify those requirements. After the 1983 collapse of the I-95 bridge over Connecticut's Mianus River, Congress required states to report “fracture-critical” bridges. And since fatal bridge collapses in Connecticut and New York in the late 1980s, states must now report scour (soil erosion that occurs underwater) levels.
We regret the loss of lives that our nation's short-sighted approach to public infrastructure breeds. We applaud our readers, who are on the front lines every day, doing their best to balance need with resources. And we hope this tragedy will help focus constituents' attention on the value of your work.General Bridge Statistics
- 596, 842: Total number of bridges nationwide, per the Federal Highway Administration's National Bridge Inventory (as of December 2006)
- 102,040: Number deemed "structurally deficient in 1997
- 75,378: Number of bridges deemed structurally deficient today (a 26% decrease)
For details on the design-build criteria MN/DOT used to award the contract for the new I-35W bridge click here Related Articles
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