A lot of bridges across the U.S. need upgrades, but the rate of repairs is going slower than ever, according to a new study.

This week, the American Road & Transportation Builders Association (ARTBA) released an analysis of federal data showing that 38 percent of all U.S. bridges—around 235,000—need repair, renovation, or even replacement. And more than 47,000 of them have a structural deficiency that requires immediate attention.

Cars, trucks, and school buses cross these 47,052 compromised structures 178 million times every day.

At the same time, the pace at which bridges are being repaired has slowed.

“Although the number of structurally deficient bridges is down compared to 2017, the pace of improvement has slowed compared to the last five years,” ARTBA stated in a report summary [PDF]. “At this rate, it would take over 80 years to make the significant repairs needed on these structures.”

A number of well-known bridges, including New York’s Brooklyn Bridge and Washington, DC’s Memorial Bridge, are among those with structural deficiencies, according to the report, and nearly two-thirds of the bridges that have been identified as structurally deficient have remained so over the five years that ARTBA has conducted the study.

“Cars, trucks, and school buses cross these 47,052 compromised structures 178 million times every day,” the association noted.

Some states are worse off than others: Nearly one in five bridges in Iowa are structurally deficient, or 4,675 total—the largest number of deficiencies reported in a single state. Pennsylvania is right behind with 3,770, but the state has improved its record, repairing around 1,200 bridges over the past five years.

Despite improvements in some areas, a reduction in federal funding for infrastructure projects is having a negative effect on repair efforts. ARTBA says federal funding declined by 20 percent between 2003 and 2017.

“Incoming revenues are not anywhere where they need to be to make all of the needed investments to keep things in a good state of repair and make some of these larger replacement and rehabilitation projects happen,” ARTBA Chief Economist Alison Premo Black said in comments to CNBC.

The repairs won’t be cheap. ARTBA puts the price tag to make all the fixes at about $171 billion.

How bad are the bridges in your state? Check out the full report, complete with a state-by-state breakdown.

(cmart7327/iStock/Getty Images Plus)