Though the NTSB has not determined the likely cause of the collapse, it did identify a design error that may have contributed to the failure.
New report on the I-35W bridge collapse revealed the financial link in the case. Reporters suggested that money concerns may have been at the root of decisions regarding maintenance of the bridge.
The I-35W Mississippi River bridge (officially known simply as 'Bridge 9340') was an eight-lane steel truss arch bridge that carried Interstate 35W across the Mississippi River in Minneapolis, Minnesota, United States. Completed in 1967 and maintained by the Minnesota Department of Transportation (Mn/DOT), the bridge was Minnesota 's fifth–busiest, carrying 140,000 vehicles daily.
The bridge catastophically failed during the evening rush hour on August 1, 2007, collapsing to the river and riverbanks beneath. Thirteen people were killed and approximately one hundred more were injured.
Already in 2006 in internal Mn/DOT documents, bridge officials talked about the possibility of the bridge collapsing and worried that it might have to be condemned.
The construction taking place in the weeks prior to the collapse included joint work and replacing lighting, concrete and guard rails. At the time of the collapse, four of the eight lanes were closed for resurfacing, and there were 575,000 pounds (261,000 kg) of construction supplies and equipment on the bridge.
The report conducted by Minneapolis law firm Gray Plant Mooty and commissioned by the state Legislature revealed that money played a role in decision-making for bridge repairs
The firm studied a number of factors including information flow, decision-making at MnDOT, the organization's structure, staffing, and use of consultants. It also examined the role of state and federal funding in the tragedy.
It learned that MnDOT acted in view of financial restraints, thus not following the organization's policies and blaming decision-making responsibility for ambiguity. The flow of information was determined as "informal and incomplete," and advice from experts was not used in an effective manner.