Bridges in New York, California, and Georgia are among U.S. spans with the most traffic from the largest ships, leaving them at potential risk from collisions, according to a report from Johns Hopkins University that follows the collapse of Baltimore’s Key Bridge in March when it was struck by a drifting containership.
The team created the risk assessment model because they believe that chances are high for another such incident, and that risk to the Key Bridge amid modern shipping traffic had been underestimated. Now, the team hopes that decision makers can strategically direct safety investments to bridges most in need.
“We’re asking, ‘What is the probability of a very large ship taking out another bridge?’ and to get at that question, the first thing we have to do is understand the actual ship traffic under major bridges across the U.S.,” Michael Shields, a Johns Hopkins University engineer specializing in risk assessment and lead investigator of the National Science Foundation supported study, said in a release.
“This traffic data suggests a relatively small number of bridges see a disproportionate amount of the largest ship traffic. It’s very clear where the heavy traffic is happening and these bridges should be prioritized for more careful and rigorous risk analysis,” Shields said.
To create the study, researchers used data mining techniques to identify the nation’s bridges that are the most vulnerable to a similar strike. First, they collected six years of U.S. Coast Guard data—logs detailing the precise location, heading, speed, and status of every ship traveling through the country’s waters on a minute-by-minute basis. Then they cross-referenced the geolocated shipping information with port data and bridge data from the National Bridge Inventory to determine which large ships passed under bridges. Finally, they built a program to analyze that data set to assess large-ship traffic under more than 200 major U.S. bridges.
The results show that three bridges had—by far—the most traffic from the very largest ships: The Verrazzano-Narrows Bridge in New York City, the Talmadge Memorial Bridge in Georgia, and two San Francisco Bay Area bridges. In addition, bridges with the most traffic from large (but not necessarily the very largest) ships include Houston’s Fred Hartman Bridge and several bridges along the Mississippi River including the Crescent City Connection in New Orleans. Meanwhile, the Francis Scott Key Bridge ranked among the top 10 bridges in very large ship traffic, with on average one ship longer than 300 meters (the size of the Dali) passing under it per day.
Shields cautioned that high ship traffic alone doesn’t necessarily mean a bridge is at high risk for collisions. Other variables that play a role include local shipping channel conditions, along with existing shipping safety practices, and individual bridge protections.
