Five Years After Collapse, MnDOT, NTSB See Progress

An Interstate 35W bridge fell into the Mississippi River on Aug. 1, 2007, killing 13 people and injuring 145 others. Building and inspection of bridges have improved since then, Minnesota’s transportation commissioner says.

Thomas K. Sorel, transportation commissioner at the helm of the Minnesota DOT, and NTSB Chair Deborah A.P. Hersman posted updates on their respective websites to memorialize the fifth anniversary of the Interstate 35W bridge collapse in Minneapolis and what has been accomplished since that tragedy.

On Aug. 1, 2007 at 6:05 p.m. local time, about 456 feet of the main span of the eight-lane bridge fell 108 feet into the Mississippi River. NTSB's final report said 111 vehicles were on that portion of the bridge when it collapsed. Sorel's comments on the fifth anniversary said the collapse significantly affected all Minnesotans and "also had a dramatic effect on the way in which we care for and manage the state's transportation infrastructure."

Sorel noted MnDOT increased its bridge maintenance staff and changed its inspections to make sure bridges with maintenance needs are identified and repaired in a timely fashion. "We have developed a system in which we integrate bridge inspection information and maintenance work. This allows us to plan and prioritize our maintenance needs as well as document and assess the benefit of the work," he wrote. "We've changed our approach in building bridges by implementing a formal bridge design peer review process. MnDOT now hires separate engineering firms to review bridge designs, a step that is intended to minimize the risk of a critical design error like the one that caused the I-35W Bridge to fail. We've also changed policies regarding storage of material on bridges under construction to ensure that the structure is not overloaded.

"We also worked hard to replace the I-35W Bridge with a new structure, built it in record time, using innovative contracting and building techniques. The result is a strong and stable structure that will serve the state for a century. And the lessons learned constructing that bridge will be used on other structures in Minnesota as well as around the nation."

Sorel wrote that, thanks to funding provided by the state legislature in 2008, 120 bridges on the Minnesota state system that need repair or replacement by 2018 have been identified. Sixty-five of those projects have been finished, 12 more will be completed by the end of 2012, and the program is on track to complete all of them by 2018, he wrote.

The safety board concluded a design error when the bridge was built caused the failure under a combination of substantial increases in the bridge's weight from previous bridge modifications, traffic, and construction materials on the bridge the day it collapsed.

Six of NTSB's safety recommendations, including new guidance for bridge owners to ensure construction loads and stockpiled materials for maintenance projects don't overload a bridge, were addressed within two years, Hersman wrote Aug. 1.

"These safety recommendations and the actions needed to complete the remaining safety recommendations will not only ensure that new bridges are being built to higher standards than their predecessors, but that all bridges will be held to that same high standard through regular inspections and maintenance," she added. "Nobody wants to see tragedy strike in such a manner ever again, and the efforts taken by the Federal Highway Administration and the American Association of State Highway and Transportation Officials to address these deficiencies provide an improved safety structure to the bridge industry that America rides on and depends on every day."

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