Highlighting the importance of maintaining infrastructure in the United States, a report from the American Road and Transportation Builders Association identified more than 47,000 bridges across the United States that are deemed structurally deficient. Although “structurally deficient” does not necessarily mean the bridges are at the brink of collapse, it does mean they need renovations or repairs to upgrade them. Bridge collapses are rare, but when they occur, they can have catastrophic consequences.

Deficient Bridges Crossed 178 Million Times Daily

The Bridge Report highlights data from the 2018 National Bridge Inventory ASCII files, which are released by the Federal Highway Administration and then analyzed by the American Road and Transportation Builders Association. According to the report, there are 47,052 structurally deficient bridges in the US—including close to 1,775 interstate highway bridges—and those structures are crossed a total of 178 million times every day. The report further notes that the average age of structurally deficient bridges is 62 years, compared with non-deficient bridges that have an average age of 40 years.

In total, there are 616,087 bridges in the US. Of those, 235,020 require some form of repair, including structural repair, replacement or rehabilitation. The association estimates the cost to fix the 235,000 bridges at $171 billion. Perhaps most concerning, however, is that the rate of repairs has slowed dramatically in the past five years.

“At [the current] rate, it would take over 80 years to make the significant repairs needed on these structures,” the American Road and Transportation Builders Association writes in its report.

In comparison, the 2017 estimate to complete repair work at that year’s pace was 37 years.

Officials Changed “Structurally Deficient” Definition

The number of structurally deficient bridges actually dropped from 2017 to 2018. In 2017, there were 54,559 bridges classed as structurally deficient, whereas in 2018 there were 47,052. That drop, however, is not necessarily due to repairs. Between the two years the Federal Highway Administration changed its definition of structural deficiency and as a result some bridges that previously fell into the structurally deficient bridge category no longer qualified.

Under the new definition, to count as structurally deficient at least one critical structural element—such as the deck, substructure, superstructure or culverts—must be rated as poor or worse condition. Without that limitation, an additional 6,533 bridges that would have qualified for the structurally deficient ranking in 2017 did not in 2018.

Bridges are ranked on a scale of 0-9, with 0 being the lowest rating. A rating of 4 or lower is considered poor, with each key element receiving a rating. Before the definition of structurally deficient was changed, a bridge simply had to have an overall evaluation of 4 or lower, or it had to have insufficient waterway openings. The new definition requires that at least one critical element has a rating of 4 or lower.

Notable Bridge Report Findings

The report notes that the states with the largest number of structurally deficient bridges are Iowa, Pennsylvania, Oklahoma, Illinois, and Missouri. Among the most well-known structurally deficient bridges are the Brooklyn Bridge in New York; the Memorial Bridge between Washington, DC and Arlington, VA; the San Mateo-Hayward Bridge across the San Francisco Bay in CA; and the Robert S. Maestri Bridge, across Lake Pontchartrain in LA.

Bridges at Risk of Closure

While “structurally deficient” may not mean a bridge is at risk of collapsing, there are bridges in danger of closing because their conditions are unsafe. Mississippi recently identified dozens of bridges that should be closed immediately due to safety hazards.

Meanwhile, almost 69,000 bridges in the US are under weight restrictions or have other restrictions designed to reduce the stress on the bridge.

“America’s bridge network is outdated, underfunded and in urgent need of modernization,” said Alison Premo Black, chief economist with the American Road and Transportation Builder’s Association.

Bridge Collapses Have Tragic Consequences

Although bridge collapses are relatively rare, they are also tragic. The Florida International University bridge collapse in 2018 killed six people when a pedestrian bridge under construction collapsed onto the road below it, crushing motorists. Engineers used a new form of construction called Accelerated Bridge Construction, which was designed to minimize risks, but at least one person noted cracking at one end of the bridge’s span.