The Francis Scott Key Bridge in Baltimore collapsed in March 2024 after being struck by a container ship. Six people were killed.

n 1991, Maryland was among the states that helped develop a test to evaluate bridges for the likelihood of collapse if they were to be struck by a ship. The risks varied according to a number of factors, including the speed of the vessels passing underneath, the depth of the water, the geometry of the bridge and what systems were in place to protect a bridge’s support structures.

Even as the vessel traffic crossing under the Key Bridge grew over the years in size and volume, increasing the bridge’s vulnerability, Maryland transportation officials never conducted such a risk assessment. An assessment by federal officials after the collapse revealed that the bridge’s risk level was almost 30 times the recommended threshold. Given that Maryland officials helped developed the test, one official said, “there’s no excuse.”

But many other states have not conducted risk or vulnerability assessments on their bridges. Investigators found that dozens of bridges in 19 states had not been assessed for risk of collapse in recent years, even though the volume of vessel traffic passing underneath these bridges suggested a strike by a ship was a distinct possibility. The National Transportation Safety Board has contacted the operators of these bridges — in most cases, state transportation departments and regional port authorities — to urge them to conduct assessments and, if needed, come up with measures to reduce the risk of collapse.