Valparaiso engineering professor: Bridge failure not an isolated incident

"It is one of the more dramatic examples in our time, and it's happened before," Leitch said.

The recent explosion of a New York City steam pipe that killed someone is an example, as is the failure of New Orleans' retaining walls during Katrina, he said.

The American Society of Civil Engineers has been warning about infrastructure wearing down and issues an annual report card about it.

Since the Minneapolis collapse, it's gone higher on the website.

"There's been a lot of press, and we're trying to draw attention to bridges," he said.

Most of the country's infrastructure -- sewers, water lines, power grids, highways -- was built in the post World War II boom, and is beginning to show its age. Most water and sewer systems leak.

Bridges are built to last about 40 years, and some were built before our highway system and incorporated in it.

And they're carrying more and heavier loads than designed to.

We're squeezing out use, "which is all well and good if you maintain them," he said.

Bridges are like cars. They need regular maintenance but eventually need replacing.

The 1967 collapse of Silver Bridge in Point Pleasant, WV., caused the government to institute bridge inspections every two years, but some inspections amount to a person with binoculars looking for rust.

"It comes down to funding, and they're very expensive," he said.

Unfortunately, many cities direct taxes to things like stadiums, "but our priorities should be our aging infrastructures," Leitch said. "We tend not to think about them much when they're working."

Upgrades to New Orleans' walls would've been cheaper in the long run.

The Minnesota bridge lacked redundancy in design, so like a bike chain, one break destroyed it. Redundant structures maintain integrity when a part breaks, like a spoke in a wheel, he said.