There is an estimated backlog of US$123 billion of rehabilitation work nationwide, says the ASCE in its 2017 Infrastructure Report Card. The research found that that 56,007 - 9.1% - of the USA's 614,387 bridge were structurally deficient last year.

Almost four in 10 of US bridges have been up for 50 years or more. "While the number of bridges that are in such poor condition as to be considered structurally deficient is decreasing, the average age of America’s bridges keeps going up and many of the nation’s bridges are approaching the end of their design life," says the report.

Among the recommendations that the ASCE says are needed in order to raise the grade is provision of increased funding from all levels of government. This would help continue reducing the number of structurally deficient bridges, decrease the maintenance backlog, and address the large number of bridges that have passed or are approaching the end of their design life. Bridge owners should consider the costs across a bridge’s entire lifecycle to make smart design decisions and prioritise maintenance and rehabilitation, says the ASCE.

Overall, US infrastructure was rated D+, the same grade as in the previous report card, which was published four years ago.