Maryland's bridges among highest in nation for large
Bridges in Maryland are among those with the highest mega- and large-ship traffic, according to data analysis by Johns Hopkins University engineers.
This past spring's Key Bridge collapse in Baltimore spurred an urgent assessment of United States bridge vulnerability, which prompted the data mining effort by the team at Johns Hopkins University.
In the case of mega-ship traffic, only bridges in New York, California, and Georgia ranked ahead of Maryland.
"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.," said Michael Shields, a Johns Hopkins University engineer specializing in risk assessment and lead investigator of the National Science Foundation-supported study.
Six months ago, the Francis Scott Key Bridge collapsed after a direct hit by a massive container ship. Johns Hopkins engineers immediately began an effort to modernize risk assessment models for U.S. bridges, believing chances are high for another such disaster, and that risks to the Key Bridge given its shipping traffic had been underestimated.
The team hopes better understanding of vulnerable bridges will help decision-makers direct safety investments more strategically to the bridges most in need of them.
"This traffic data suggests a relatively small number of bridges see a disproportionate amount of the largest ship traffic," Shields said. "It's very clear where the heavy traffic is happening and these bridges should be prioritized for more careful and rigorous risk analysis."
Six years of U.S. Coast Guard records provided the data for this study to determine which bridges have the most large-ship traffic. The team studied logs detailing the precise location, heading, speed, and status of every ship traveling through the country's waters on a minute-by-minute basis. They used port data and bridge data from the National Bridge Inventory to cross-reference geolocated shipping information to determine which large ships passed under bridges.
Next, they built a program to analyze the massive data set for large-ship traffic under more than 200 major U.S. bridges.
"Until the Key Bridge collapsed, there wasn't a significant impetus to ask how many large ships pass under these enormous bridges," Shields said. "Nothing like this has been done on a national scale."
The Verrazzano-Narrows Bridge in New York City, the Talmadge Memorial Bridge in Georgia, and two San Francisco Bay Area bridges topped, by far, the list of bridges with the most traffic from the very largest ships. 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.
The Francis Scott Key Bridge, before it fell, 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.
High traffic doesn't necessarily correlate with high risk for collisions, Shields said. Other factors, such as local shipping channel conditions, shipping safety practices, and individual bridge protections also play an important role.
The team's full analysis is available for download at this link . This JHU engineering site includes traffic trend data for more than 200 bridges, and results will be updated regularly.
Studying bridge collision vulnerability will continue to be a major focus of the team, and they will begin to determine how often ships that pass under these bridges stray off course. This will allow them to determine the aberrancy rate for ships in the U.S., and the aberrancy rate near highly trafficked bridges.
They will look closely at the Key Bridge to determine what the ship traffic and aberrancy rate suggested about the likelihood of that collision.
"Was it an exceedingly rare event that couldn't have been predicted," Shields said, "or not as surprising as we might have thought?"
The team expects to release further findings in 2025.
The team included structural engineer Ben Schafer, the Willard and Lillian Hackerman Professor; Rachel Sangree, a structural engineer with bridge inspection experience; Promit Chakroborty and Damir Akchurin, PhD. students in Civil and Systems Engineering; Johns Hopkins undergraduate and master's students Diran Jimenez, Natalia Dougan, Yile Wang, Jenna Halpin, and Diana Arizmendi; and Morgan State undergraduate Esther Ezeigbo.
