By Jill Rosen
Ships are highly likely to collide with major bridges across the United States, with potentially catastrophic collisions happening every few years, according to preliminary findings of an urgent assessment of the nation’s bridge vulnerability following the 2024 Key Bridge collapse in Baltimore.
Though ship strikes should be extremely rare—and bridge design standards stipulate that the annual chances of a bridge collapse from ship collision should be less than 1 in 10,000—some of the nation’s busiest bridges will likely be hit by ships within our lifetime, according to the findings released today by Johns Hopkins University. The most vulnerable bridges, including the Huey P. Long Bridge outside New Orleans and the San Francisco-Oakland Bay Bridge, are likely to be hit by a ship within about 20 years, the study found.
“With this investigation we wanted to know if what happened to the Key Bridge was a rare occurrence. Was it an aberration? We found it’s really not,” said Michael Shields, a Johns Hopkins engineer specializing in risk assessment and lead investigator of the National Science Foundation–supported study. “In fact, it’s something we should expect to happen every few years.”
A year ago, Baltimore’s Francis Scott Key Bridge collapsed after a direct hit by a massive container ship. Believing chances were high for another such incident, and that risk to the Key Bridge amid modern shipping traffic had been underestimated, Johns Hopkins engineers immediately launched a risk assessment for U.S. bridges.
The team aimed to estimate the actual chances a large ship would hit the country’s most significant bridges.
They collected and mined 16 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. They cross-referenced the geolocated shipping information, hundreds of millions of data points, with port data and bridge data from the National Bridge Inventory to determine which large ships passed under bridges.
Using this traffic data, along with ship aberrancy rates adopted from the American Association of State Highway and Transportation Officials, the researchers estimated the probability of very large ships colliding with the piers of major bridges across the U.S.
The results revealed stark vulnerabilities for many bridges. Several bridges could expect a major ship collision—a collision strong enough to cause catastrophic damage or collapse—at least once every 20 to 50 years. Many others are likely to sustain a ship strike within 100 years.
The Key Bridge would have been among the 10 most vulnerable bridges in the country, according to the team’s calculations. They predicted it would have likely been hit by a ship within 48 years. The bridge was 46 years old when it fell – and it had sustained a minor hit from a ship previously.
“To keep our bridges safe and operational, we want the chances of a collision strong enough to take down the bridge to be less than one in 10,000 in a given year, not one in a 100. One in 100 is extremely high,” Shields said. “If I look at the San Francisco Bay Bridge, we’re likely to see a major collision once every 22 years. That is huge. We want that number to be thousands of years. That’s tens of years.”
According to preliminary results, the most vulnerable bridges are:
- Huey P. Long Bridge, Louisiana: Collision expected once every 17 years.
- San Francisco–Oakland Bay Bridge: Collision expected once every 22 years.
- Crescent City Connection, New Orleans: Collision expected once every 34 years.
- Beltway 8 Bridge, Texas: Collision expected once every 35 years.
- Hale Boggs Memorial Bridge, Louisiana: Collision expected once every 37 years.
- Bayonne Bridge, N.Y./N.J.: Collision expected once every 43 years.
- Fred Hartman Bridge, Texas: Collision expected once every 47 years.
- Martin Luther King Bridge, Texas: Collision expected once every 64 years.
- Sunshine Bridge, Louisiana: Collision expected once every 71 years.
- Rainbow Bridge, Texas: Collision expected once every 71 years.
- Veterans Memorial Bridge, Louisiana: Collision expected once every 74 years.
- Chesapeake Bay Bridge, Maryland: Collision expected once every 86 years.
- Talmadge Memorial Bridge, Georgia: Collision expected once every 88 years.
- Veterans Memorial Bridge, Texas: Collision expected once every 94 years.
- Delaware Memorial Bridge, Del./N.J.: Collision expected once every 129 years.
- Dames Point Bridge, Florida: Collision expected once every 152 years.
- Horace Wilkinson Bridge, Louisiana: Collision expected once every 198 years.
- Verrazzano-Narrows Bridge, New York: Collision expected once every 362 years.
- Golden Gate Bridge, California: Collision expected once every 481 years.
- John A. Blatnik Bridge, Minnesota/Wisconsin: Collision expected once every 634 years.
Some bridges with considerable traffic from large ships did not make the list because their piers are safely on land, away from the passing ships. Those include Minnesota’s Duluth Lift Bridge and the Vincent Thomas Bridge in California.
Because no two bridges are the same, what happens in the event of a collision is very different from bridge to bridge, Shields said.
While a large ship collision would not necessarily result in a bridge collapse, Shields said it would almost certainly cause irreparable damage and very likely cause at least a partial collapse.
“If one of these massive ships hits a bridge, it’s catastrophic,” he said.
To lower the risk for these bridges, the critical thing is to keep ship traffic away from the piers, and to outfit them with robust protections including dolphins and other structures that keep ships from approaching the piers.
“There’s still a lot of uncertainty in predicting the frequency of ship collisions, even with the best data we have,” he said. “But the important point is not whether it will occur every 17 years or every 75 years– it’s that it’s happening way too often.”
The team included structural engineer Ben Schafer, the Willard and Lillian Hackerman Professor; Rachel Sangree, a structural engineer and teaching professor with bridge inspection experience; Promit Chakroborty and Damir Akchurin, PhD students in Civil and Systems Engineering; Adwait Sharma, postdoctoral fellow in Civil and Systems Engineering; Johns Hopkins undergraduate and master’s students Diran Jimenez, Natalia Dougan, Yile Wang, Jenna Halpin, Diana Arizmendi, Lemon Doroshow, Yun Tang, JunYup Kim, Alek Ding, and Ololade Akinbamilowo; and Morgan State undergraduate Esther Ezeigbo.
This article was originally published by Johns Hopkins University.
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