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Causes of Bridge Failures

August 2, 2007

There are about 600,000 bridges in the United States with 500,000 of them over water. "The cause of the I-35W bridge collapse in Minnesota over the Mississippi River is not known, and it will be awhile before that will be determined," says Jean-Louis Briaud, a bridge expert with the Texas Transportation Institute.

Between 1966 and 2005, there have been approximately 1500 bridge collapses in the U.S. and those causes are documented. "In terms of causes of bridge failures, historically scour (soil erosion around bridge pilings) accounts for about 60 percent of collapses (also called hydraulic). A distant second involves ship collisions at 12 percent."

The following graph shows the causes of bridge collapses in the U.S.

Graph highlighting causes for 1502 bridge failures between 1966 and 2005. Hydraulic conditions account for about 60%. Overload and Collision follow Hydraulic at under 15% each. Other causes include: miscellaneous, fire, steel, natural, earthquake, deterioration, concrete, and construction.

"It is not possible to design a bridge that will have a zero risk of failure," Briaud says. "There are simply too many variables and sometimes there are extraordinary conditions that can not be anticipated."

Traveling across bridges is very safe in comparison to other forms of transportation. Bridge collapses account for only a few dozen deaths each year. "More than 40,000 people die in car accidents every year, and several hundred are killed in airplane crashes. In a broader context, 600,000 people die from cancer each year," Briaud says.

Causes of Bridge Failures (summary) PDF document - For best results, view PDF files with the most recent version of the Adobe Acrobat Reader

For More Information

Jean-Louis Briaud, Ph.D., P.E.
ph. (979) 845-3795
TTI Public Affairs
ph. (979) 862-3763

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