The disastrous collapse of the I-35 bridge in Minneapolis on Aug. 1, 2007, has gripped the nation not only because of the loss of life, but because of the questions it raises as to the integrity of other highway structures. Claim personnel who deal with both large and small losses are familiar with the aftermath procedure of attempting to determine the cause of the loss, or in this case, the collapse of the bridge.

The National Transportation Safety Board (NTSB), the governmental agency tasked with transportation-related investigations, has indicated that the findings as to the cause of the collapse will probably not be available for about a year, which is typical of large losses. Data must be gathered, bridge sections in the Mississippi must be retrieved, and failure analyses must be performed in order to arrive at a probable scenario on what caused the collapse. Despite the long time required for a full reconstruction of the accident, the Internet is overflowing with failure analyses from a variety of sources ranging from non-scientific bloggers to college professors. In order to cut through the chatter, here is what is known at this time regarding the failure.

Bridge construction started in 1964, and was completed in 1967. It had a total length of 1,907 feet, with three lanes in each direction. The bridge was heavily traveled, carrying 140,000 vehicles daily. Due to its proximity to St. Anthony Falls to the west, the bridge receives constant moisture f, which causes considerable driving difficulty in the winter. An automatic de-icing system was installed in the bridge deck in 1999, using potassium acetate solution as the ice melting agent. At 6:05 p.m. on Aug. 1, 2007, the bridge collapsed without warning.