The pace of improving the nation’s inventory of structurally deficient bridges slowed slightly in the past year, the study found. At the current pace of repair or replacement, it would take 37 years to remedy all of them, said Dr Alison Premo Black, chief economist for the American Road & Transportation Builders Association (ARTBA), who conducted the analysis.

The ARTBA analysis of the latest federal data shows that 54,259 of the country’s 612,677 bridges are rated ‘structurally deficient’. The average age of a structurally deficient bridge is 67 years, compared to 40 years for non-deficient bridges.

Overall, there are identified repair needs for one in three (226,837) US bridges; the figure is also one in three for the 17,726 interstate highway bridges in need of repair.

The report finds that there is the equivalent of one bridge rated ‘structurally deficient’ for every 43.5km, on average, of the major highway network.

“An infrastructure package aimed at modernising the interstate system would have both short- and long-term positive effects on the US. economy,” said Black. Traffic bottlenecks, she said, cost the trucking industry alone over US$60 billion per year in lost productivity and fuel, which “increases the cost of everything we make, buy or export".

To help ensure public safety, bridge decks and support structures are regularly inspected for deterioration and remedial action. They are rated on a scale of zero to nine - with nine meaning the bridge is in “excellent” condition.  A bridge is classified as structurally deficient and in need of repair if the rating on a key structural element is four or below.