WASHINGTON (Reuters) - More than 63,000 bridges across the United States are in urgent need of repair, with most of the aging, structurally compromised structures part of the interstate highway system, an analysis of recent federal data has found.

Cars are seen in the water as a span of highway bridge sits in the Skagit River May 24, 2013 after collapsing near the town of Mt Vernon, Washington late Thursday. REUTERS/Cliff DesPeaux

The report, released on Thursday by the American Road and Transportation Builders Association, warned that the dangerous bridges are used some 250 million times a day by trucks, school buses, passenger cars and other vehicles.

The group, which represents the U.S. transportation construction market, analyzed recent U.S. Department of Transportation data for its study.

Pennsylvania led the list of structurally deficient bridges, with 5,218, followed by Iowa, Oklahoma, Missouri and California.

Nevada, Delaware, Utah, Alaska and Hawaii had the least.

Overall, there are more than 607,000 bridges in the United States, according to the DOT’s Federal Highway Administration, and most are more than 40 years old.

The Transportation Department routinely inspects bridges and rates them on a scale of zero to nine. Bridges receiving a grade of four or below are considered structurally deficient, and now account for more than 10 percent of all bridges.

States rely heavily on federal funds to pay for road and bridge projects but could face funding shortfalls by late August as the federal Highway Trust Fund draws closer to insolvency without congressional action.

The fund, bankrolled by an 18.4 cents-a-gallon tax on gasoline and 24.4 cents-a-gallon tax on diesel, is expected to run out of money by 2015 as fuel use in America stagnates.

“Letting the Highway Trust Fund go insolvent would have a devastating impact on bridge repairs,” said Alison Premo Black, chief economist at ARTBA.

A temporary measure that provided funding for road and bridge projects for two years is set to expire in September, and the transportation industry has urged Congress to act quickly to keep the funds flowing.

“The bridge problem sits squarely on the backs of our elected officials,” Black said. “The state transportation departments can’t just wave a magic wand and make the problem go away.”

The American Society of Civil Engineers, which separately produces a report card on U.S. infrastructure every four years, gave it an overall “D,” or poor, grade. Bridges received a “C+” grade for mediocre.

The U.S. needs to invest $20.5 billion annually to clear the bridge repair backlog, up from the current $12.8 billion spent annually, the ACSE has said.

The civil engineers’ group estimates that the U.S. will need to invest $3.6 trillion by 2020 to keep its transportation infrastructure in a good state of repair.