Numbers can never match the horror of Wednesday's Minnesota highway collapse, but the statistics on deficient bridges are staggering.
Thirteen percent of bridges in the United States share the same "structurally deficient" rating as the bridge that collapsed in Minneapolis, including 30 percent of bridges in Oklahoma, 26 percent in Rhode Island, and 25 percent in Pennsylvania. It could not immediately be determined how many bridges are currently closed across the country as unsafe, and the U.S. Department of Transportation didn't return calls seeking comment today.
Minnesota's bridges are actually some of the country's safest: Only 12.2 percent of the state's bridges are rated "structurally deficient" or "functionally obsolete," ranking it third best behind Arizona (10 percent) and Nevada (12 percent), according to 2006 data from the Bureau of Transportation Statistics.
Only 8.8 percent of Minnesota's bridges are, like the collapsed I-35W span, rated "structurally deficient," the 14th lowest total in the country.
Overall the data indicates that 26.2 percent of the nation's bridges are in need of repair or do not meet the highest safety standards. Bridges in this category are rated either structurally deficient or functionally obsolete, according to the statistics.
Washington, D.C., has the country's least safe bridges, with 63 percent of the district's 245 bridges rated either structurally deficient or functionally obsolete.
A bridge is rated "structurally deficient" if it's in poor condition and is deemed ill-equipped to handle the demands of the traffic load it carries, according to Susan Lane, manager of codes and standards with the American Society of Civil Engineers, which evaluates bridge safety.
Structurally deficient bridges don't need to be closed, though they usually do require some repairs or weight restrictions, said Steve Chizmar, a spokesman for the Pennsylvania Department of Transportation.
A span is "functionally obsolete" if it fails to meet certain traffic standards, Lane said. For example, the bridge may be too narrow to hold both traffic lanes and shoulders, or it may hang too low, leaving inadequate clearance for trucks and trailers on a roadway below.
The federal government requires states to inspect bridges at least once every two years, with many the details of the inspection left to the states.
There are three components to bridge inspections, Lane said, including evaluations of the substructure (the part of the bridge under water), the superstructure (the structural part above water), and the road deck. Each part receives a rating on a 1-10 scale and then may be labeled deficient or obsolete, she said.
Among states, Rhode Island ranks last, with 55 percent of its 749 bridges rated either deficient or obsolete, followed by 52 percent of the 4,919 bridges in Massachusetts and 47 percent of Hawaii's 1,104 bridges, according to the government data.
Texas has the most bridges in the United States at 49,226 but it rates 15th best with only 21 percent either deficient or obsolete. It is fourth best when just considering structurally obsolete bridges: only 4.8 percent of its bridges receive that rating.
Chizmar said that even if a bridge receives a "structurally deficient" rating, it's still safe for most uses. One in four of Pennsylvania's 22,291 bridges are structurally deficient, according to the federal government numbers.
"The bottom line is a structurally deficient bridge is not unsafe," Chizmar said. He said that while these bridges normally do require repair, the overwhelming majority remain in service, perhaps with some traffic and weight restrictions.
From 2005 to 2006 nearly $985 million was spent on Pennsylvania on a total of 1,533 bridge projects, Chizmar said. But with 5,532 structurally deficient bridges and another 4,028 functionally obsolete bridges, these numbers indicate that only a fraction of problematic bridges received repairs.
He estimated that approximately 52 bridges in the state have been closed because they are unsuitable for travel.