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Over the past decade, there has been increased awareness of the significance of bridges to our nation’s economy and the safety of the traveling public. At all levels of government, a concerted effort has been made to reduce the number of structurally deficient bridges in the U.S.—bridges that require significant maintenance, rehabilitation, or replacement. Structurally deficient bridges are not unsafe, but could become so and need to be closed without substantial improvements.

As of 2016, one in 11 (9.1%) of bridges were designated structurally deficient, which represents an improvement from a decade ago when 12.3% of bridges were structurally deficient. As bridges greatly vary in size, the percentage of deck area that belongs to structurally deficient bridges is another useful indicator. 6.3% of total bridge area belonged to structurally deficient bridges in 2016, an improvement from 9.5% in 2007. Encouragingly, higher traffic volume bridges are less likely to be structurally deficient. Yet, on average, there were 188 million trips across a structurally deficient bridge each day in 2016. Some states are doing better than others at maintaining, repairing, or replacing their bridges. The percentage of bridges that are structurally deficient ranged from 1.6% in Nevada to 24.9% in Rhode Island in 2016.

Of the 614,387 bridges in the National Bridge Inventory, almost four in 10 (39%) are over 50 years or older, and an additional 15% are between the ages of 40 and 49. The average bridge in the U.S. is 43 years old. Most of the country’s bridges were designed for a lifespan of 50 years, so an increasing number of bridges will soon need major rehabilitation or retirement.

As part of a bridge’s regular inspection, it may be determined that the bridge can only carry traffic up to a certain weight or speed, requiring posting of a load restriction. One in 10 (10.1%) bridges had such restrictions in 2016. Posted bridges can dramatically increase driving time for larger vehicles such as school buses, ambulances, and delivery trucks. Bridges that do not serve current traffic demand or meet current standards, whether due to too few lanes or too narrow lanes or shoulders, are considered functionally obsolete. More than one in eight (13.6%) bridges in the U.S. were functionally obsolete in 2016. (NB: if a bridge is both functionally obsolete and structurally deficient, it is only counted as structurally deficient.) These bridges frequently act as choke points and can increase congestion.

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