By Ian Simpson

WASHINGTON (Reuters) - Almost 56,000 U.S. bridges are structurally deficient, down slightly from a year ago, with underperforming spans including New York's landmark Brooklyn Bridge, accord to a construction industry report released on Wednesday.

About 1,900 structurally deficient bridges are on interstate highways and vehicles cross underperforming U.S. spans 185 million times a day, the analysis of federal data by the American Road and Transportation Builders Association found.

Rebuilding U.S. infrastructure, including bridges, was a campaign promise of Republican President Donald Trump, who has backed a $1 trillion infrastructure plan over a decade.


The U.S. highway system "is outdated, overused, underfunded and in desperate need of modernization," Alison Premo Black, the association's chief economist, said in a statement.

The group's report was based on an analysis of data from the U.S. Department of Transportation’s 2016 National Bridge Inventory.

The builders' group said 55,710 bridges, or about 9 percent of U.S. spans, were structurally deficient, a share that is down 0.5 percent from a 2015 bridge report.

"While these bridges may not be imminently unsafe, they are in need of attention," the group said.

Of the most-traveled underperforming bridges, the top 14 are in California. No. 1 is the Interstate 110 bridge over Los Angeles County's Dominguez Channel, which vehicles cross 274,000 times a day.

State estimates put the cost of repairing underperforming U.S. bridges at more than $700 billion, Black said in a telephone interview.

"I'd say that's conservative," she added.

A bridge is classified structurally deficient if one or more of the key bridge elements, such as the deck, superstructure or substructure, is in "poor" or worse condition.

The Brooklyn Bridge, a New York suspension bridge built in 1883, is among the state's most-traveled underperforming spans. The landmark structure crossing New York's East River is listed as an urban freeway or expressway with 134,000 daily crossings.

Among states, Iowa had the most structurally deficient bridges, at 4,968. Nevada had the fewest, at 31.

At least 15 percent of bridges in eight states fell in the underperforming category, with Rhode Island heading the list with a quarter structurally deficient.

(Reporting by Ian Simpson; Editing by Andrew Hay)