Michigan motorists shouldn't second-guess crossing the state's bridges, despite the state's percentage of "structurally deficient" bridges, experts say.

The Interstate 35W bridge that collapsed Wednesday in Minnesota was named "structurally deficient" two years ago. Michigan has the 10th highest percentage of structurally deficient bridges in the country at 16 percent, more than 3 percent above the national average.

"Structurally deficient" does not mean a bridge is unsafe, said Michigan Department of Transportation, or MDOT, spokeperson Kari Arend.

"Generally some kind of small repair is needed for that bridge," she said.

Currently, Michigan has four bridges - all located in northern Michigan - that are similar in structure to the bridge in Minneapolis, Arend said. Three are vehicular and one is pedestrian.

When states name bridges safe or unsafe, a comprehensive look is used to consider the entire bridge, down to the guard rails.

"They've all been recently inspected," she said. "And we are going out to reinspect them starting tomorrow."The amount of funding to repair the state's bridges averages more than $180 million a year, Arend said.

Venkatesh Kodur, an MSU engineering professor dissuaded the state's drivers from panicking.

"People don't have to think twice or worry when they're crossing a bridge," Kodur said.

Michigan bridges are designed and monitored well, and if a bridge is deemed unsafe, MDOT would close it immediately, Kodur said.

Michigan's 10th highest percentage of structurally deficient bridges compares to Minnesota's 8.7 percent, which ranks 36th.

Kodur questioned the fairness of ranking the number of states' deficient bridges to determine the safety of each state's bridges. Michigan bridges perform just as well as other states, he said, despite facing conditions that accelerate bridge decay.

The state's bridges experience more extreme variations in temperature and use of salt for icy roads, both of which wear on bridges, Kodur said.

Michigan's bridges are required to be inspected at least once every two years, Arend said.

"All of our bridges are safe in Michigan," she said.

Rigoberto Burgueño, another MSU engineering professor, was taken back by the bridge collapse.

"I was very surprised to see a failure of this type without an apparent cause because it's very rare, especially understanding how closely-monitored these bridges are," Burgueño said.

Kodur went further, saying he was "shocked" by the catastrophe.

"This collapse wasn't 'infrequent,' or 'just rare,'" he said. "It is extremely rare. We have tens of thousands of bridges in the U.S. and this happened to one bridge."

Kodur was glued to the television after hearing the news.

"It was shocking," he said. "We build with a lot of factors in mind dealing with safety, so my immediate thought was, 'How can this happen?'"

Most of the country's bridges were built in the 1950s and 60s, Kodur said, making them due for careful examination.

"With any structures, once they surpass 40, 50 or 60 years old, you need to monitor and look after them," he said.

Burgueño said the bridge Michiganders might be most familiar with, the Mackinac Bridge, is not structurally comparable to the bridge in Minneapolis.

Other bridges that were built within a few years of the bridge in Minneapolis are unique and mature at different rates.

"Even if two bridges were built the same, one in Minneapolis and one here, the two would age differently," he said.

Burgueño, who teaches a course on bridge design, didn't want to speculate reasons for the failure of the bridge but ruled out too much traffic. While the bridge may have been jammed with rush-hour traffic, the number of cars on the bridge were "small" compared to its capacity, he said.

"Such sudden events aren't typically induced by the amount of traffic, so something else caused this sudden collapse," he said.

Kodur expects the cause of the collapse will surface within the next few weeks. He aided in a 9/11 investigation - one of the country's last major structural disasters.

The professor investigated causes for the World Trade Center's collapse as a member of an expert team that later presented its findings to a congressional committee.

Kodur called for the state to re-evaluate the amount of resources invested in the department of transportation, saying Wednesday was a "wake-up call."

Arend said that the number of bridge inspectors is constantly increasing in Michigan.

"We had six in 1997," she said. "And we've since increased that number to 20."

Burgueño was comfortable with how much priority is put on monitoring state bridges.

"As infrastructures are getting older, our society's demand for renewing them are getting more stringent."

Staff writer Ryan Beene contributed to this report.