(CNN) There are over 612,000 bridges in the United States. Almost 10% of them need to be repaired or replaced.

That adds up to 55,710 bridges, according to a report on the state of the nation's roads and bridges from the American Road and Transportation Builders Association (ARTBA).

The states with bridges in the worst shape? Iowa, Pennsylvania, Oklahoma, Missouri, and Nebraska.

Americans cross these structures in disrepair 185 million times a day.

What structurally deficient means

The report, released Wednesday , ranks bridges on their structural deficiency.

"If the bridge is structurally deficient, one of the key elements is below a 4 on a scale from 0 to 9, meaning poor or worse condition," Alison Black, the transportation association's chief economist and author of the report, told CNN. "It doesn't mean the bridge is unsafe, but it does mean that the bridge is in need of repair."

Maybe not unsafe, but still urgent. According to Black, outdated and deteriorating bridges cause road closures and limit access for cargo trucks. It's not just an inconvenience, it's keeping the shipping industry down.

Good news, bad news

There is some good news, though.

The association has been actively pushing to keep this problem from being swept under the rug by both local and federal governments, and there has been a 4.8% improvement as a result.

The bad news is the numbers aren't going down fast enough. Black estimates it'll take 20 more years to repair all the bridges on the list.

Even popular bridges like the Arlington Memorial Bridge and the Brooklyn Bridge are among the roadways suffering from underfunding and decay.

JUST WATCHED Millions drive over structurally deficient bridges daily Replay More Videos ... MUST WATCH Millions drive over structurally deficient bridges daily 04:29

What comes next

The prescription for the ailing bridge system is a two-step process: finance, then modernize. "If we are going to lay that foundation for economic growth, we need to invest in a modernized highway system," Black said.

Finally, if you live in Washington D.C., Nevada, Delaware, Hawaii, or Utah, take heart. These states have the fewest deficient bridges.