Some of the busiest bridges in the U.S. will be hit by ships in our lifetime, Johns Hopkins University study finds
A study by Johns Hopkins University found that ships are highly likely to collide with major bridges in the U.S., causing catastrophic damage every few years.
The study, which detailed the vulnerability of bridges across the nation, was released almost one year after the collapse of Baltimore's Francis Scott Key Bridge.
According to the study, some of the busiest bridges in the country will be hit by ships in our lifetime, though bridge design standards dictate that the annual chances of a bridge collapse from a ship collision should be less than 1 in 1,000.
Maryland's Chesapeake Bay Bridge ranked 12th for risk out of 20 bridges studied.
"(It's) quite significant, much higher than we would want it to be," said Michael Shields, a Johns Hopkins engineer specializing in risk assessment and lead investigator of the National Science Foundation–supported study.
Most vulnerable bridges for ship-strikes
After the collapse of the Key Bridge on March 26, 2024, Johns Hopkins University researchers aimed to determine the chances of a large ship hitting the country's most significant bridges.
"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," Shields said.
"In fact, it's something we should expect to happen every few years," he added.
The study found that the most vulnerable bridges in the U.S. include the Huey P. Long Bridge in Louisiana and the San Francisco-Oakland Bay Bridge. Both are likely to be hit by a ship within about 20 years, according to the study.
The study found the following bridges are also among the most vulnerable:
- Collisions at the Bayonne Bridge between New York and New Jersey are expected once every 43 years
- Collisions at the Chesapeake Bay Bridge in Maryland are expected once every 86 years
- Collisions at the Delaware Memorial Bridge between Deleware and New Jersey are expected once every 129 years
- Collisions at the Verrazzano-Narrows Bridge in New York are expected once every 362 years
"We want the collision probabilities themselves, the collision chances, to be on the order of centuries not decades," Shields said.
What the bridge-strike study is based on
Researchers collected 16 years of U.S. Coast Guard data to conduct the study. The data consisted of the locations, speed and status of every ship that travels through the country's waters along with data on ports and bridges.
Researchers were then able to estimate the probability of very large ships colliding with the piers of major bridges.
The study found that many of the nation's bridges have vulnerabilities and several bridges could expect a major ship collision at least once every 20 to 50 years. Others are more likely to be struck by a ship every 100 years.
According to the study, the Key Bridge would have been one of the 10 most vulnerable bridges in the country, as researchers predicted it would have likely been hit by a ship within 48 years.
The Key Bridge was 46 years old when it fell in 2024. It had previously sustained a minor ship collision.
How to lower ship-strike risk for bridges
"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 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."
Although a collision by a large ship would not always result in a bridge collapse, the study found it would "almost certainly" cause irreparable damage and likely cause at least a partial collapse.
To lower the risk of a bridge collapse, the study determined that ship traffic should be diverted away from piers. The piers should also be equipped with protections including dolphins and other structures that keep ships from getting too close to piers.
"There's still a lot of uncertainty in predicting the frequency of ship collisions, even with the best data we have," Shields 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."
What happened to the Key Bridge?
On March 26, 2024, the container ship Dali lost power before crashing into the bridge, killing six construction workers who were thrown into the Patapsco River.
The NTSB's initial investigation showed a series of power failures on Dali as it departed the Port of Baltimore. The report revealed the ship experienced four outages in a span of less than 12 hours, which left the ship unable to maneuver and avoid the bridge.
The victims were identified as 35-year-old Alejandro Hernandez Fuentes; 26-year-old Dorlian Ronial Castillo Cabrera; 38-year-old Maynor Yasir Suazo-Sandoval; 24-year-old Carlos Hernandez; 49-year-old Miguel Angel Luna Gonzalez; and 35-year-old Jose Mynor Lopez.
The National Transportation Safety Board (NTSB) recently blamed the Maryland Transportation Authority (MTDA) for not assessing the risk of structural damage to the Key Bridge well before it collapsed.
NTSB: Key Bridge collapse risk was high
NTSB chair Jennifer Homendy said a vulnerability assessment would not have prevented the collapse, but other safety measures could have been put in place to avoid the tragedy.
"We conclude in our report that had the MDTA conducted a vulnerability assessment of the Key Bridge based on recent vessel traffic, the MDTA would have been able to proactively identify strategies to reduce the risk of a collapse and loss of lives associated with a vessel collision with the bridge," Homendy said.
According to the NTSB, the American Association of State Highway and Transportation issued safety recommendations for the Key Bridge in 1991 and 2009 but those recommendations were never executed.
"Had MDTA conducted the assessment based on recent vessel traffic, the MDTA would've been able to reduce the risk of collapse and loss of life," Homendy said.
Homendy said the NTSB findings revealed the level of risk for a catastrophic collapse was nearly 30 times higher than acceptable risk levels for the Key Bridge and 15 times higher, specifically for Pier 17, one of the bridge's main pillars that was struck by the cargo ship.
The agency released more than 1,000 pages of investigative documents on Thursday including interviews and the bridge factual report.
The NTSB says it will release more reports in the coming weeks with the final report expected in the fall.
Needing a vulnerability assessment
The NTSB told 30 owners of 68 bridges across 19 states to conduct a vulnerability assessment to determine the risk of a bridge collapse from a vessel collision.
The Chesapeake Bay Bridge in Annapolis was among those bridges listed in the NTSB report that was told to have a vulnerability assessment. The NTSB says the MDTA has yet to conduct a vulnerability assessment and calculation on this bridge, which has similar vessel traffic to the Key Bridge.
The NTSB mentioned that their recommendation does not suggest that the 68 bridges are certain to collapse, but rather those bridge owners should evaluate whether the bridges are above the American Association of State Highway and Transportation Officials' acceptable level of risk.
The 68 bridges were divided into two categories, "critical/essential" and "typical." Those deemed critical/essential are those that serve as "important links." The Key Bridge had this classification. Those that are not deemed critical/essential fall under the typical designation.
"As for the existing bridge, we know that they have not done that," Homendy said. "That vulnerability assessment takes a long time. There's no reason why they shouldn't have done it before now. It shouldn't take an urgent safety recommendation to take action and we expect that to be done now."'
The bridges recommended for a vulnerability assessment are listed here.
