Bay Bridge At High Risk Of Collapse If Hit By Ship, New Study Shows

The Johns Hopkins report came on the heels of a National Transportation Safety Board report last week that documented dozens of other bridges across that country that are also at risk of collapse should a vessel collide with them.

As a result, the NTSB is recommending that 68 bridges undergo a vulnerability assessment to determine the risk of collapse. In Maryland, the Chesapeake City Bridge and both spans of the Bay Bridge are recommended to undergo a risk assessment.

The most vulnerable U.S. bridge is the Huey P. Long Bridge outside New Orleans, which the report said is likely to be hit by a ship once every 17 years. The San Francisco-Oakland Bay Bridge is vulnerable to a ship collision every 22 years, the report said.

“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,” Michael Shields, a Johns Hopkins engineer specializing in risk assessment and lead investigator of the National Science Foundation–supported study, said in a news release. “In fact, it’s something we should expect to happen every few years.”

After the Key Bridge collapse, which killed six construction workers and resulted in about $1.9 billion in damage, Shields and his team believed the chances for another such incident were higher than previously thought.

“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,” according to a summary of the study.

The results revealed stark vulnerabilities for many bridges, researchers said. Several bridges could expect a major ship collision — one 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.

According to the preliminary results of the Johns Hopkins study, the most vulnerable bridges are:

1. Huey P. Long Bridge, Louisiana: Collision expected once every 17 years
2. San Francisco–Oakland Bay Bridge: Collision expected once every 22 years
3. Crescent City Connection, New Orleans: Collision expected once every 34 years
4. Beltway 8 Bridge, Texas: Collision expected once every 35 years
5. Hale Boggs Memorial Bridge, Louisiana: Collision expected once every 37 years
6. Bayonne Bridge, N.Y./N.J.: Collision expected once every 43 years
7. Fred Hartman Bridge, Texas: Collision expected once every 47 years
8. Martin Luther King Bridge, Texas: Collision expected once every 64 years
9. Sunshine Bridge, Louisiana: Collision expected once every 71 years
10. Rainbow Bridge, Texas: Collision expected once every 71 years
11. Veterans Memorial Bridge, Louisiana: Collision expected once every 74 years
12. Chesapeake Bay Bridge, Maryland: Collision expected once every 86 years
13. Talmadge Memorial Bridge, Georgia: Collision expected once every 88 years
14. Veterans Memorial Bridge, Texas: Collision expected once every 94 years
15. Delaware Memorial Bridge, Del./N.J.: Collision expected once every 129 years
16. Dames Point Bridge, Florida: Collision expected once every 152 years
17. Horace Wilkinson Bridge, Louisiana: Collision expected once every 198 years
18. Verrazzano-Narrows Bridge, New York: Collision expected once every 362 years
19. Golden Gate Bridge, California: Collision expected once every 481 years
20. John A. Blatnik Bridge, Minnesota/Wisconsin: Collision expected once every 634 years

For the study, the Johns Hopkins engineers 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, researchers estimated the probability of very large ships colliding with the piers of major bridges across the country.

Those calculations would have put the Key Bridge among the 10 most vulnerable U.S. bridges, researchers said. 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 previously survived a minor hit from a ship.

“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 in the release. “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.”

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, it would almost certainly cause irreparable damage and very likely cause at least a partial collapse, he said.

“If one of these massive ships hits a bridge, it’s catastrophic,” he said.

To lower the collision risk, ship traffic must be kept away from piers, which should be outfitted with dolphins and other structures to keep ships from approaching the piers, researchers said.

“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.”

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