Study names bridges most likely to collapse from boat collisions

Fears of boat collisions with bridges have run high since a container ship hit the Francis Scott Key Bridge in Baltimore last year, collapsing the bridge and killing six people.

Now, a study from John Hopkins University shows just how risky these collisions are among the nation's biggest 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,” said Michael Shields, a Johns Hopkins engineer specializing in risk assessment and lead investigator of the National Science Foundation, said in comments with the study.

Some of the nation's busiest bridges will likely suffer a boat collision, at least once, that can cause catastrophic damage or collapse within 20 to 50 years, despite being designed to keep collapses to a less than 1 in 10,000 chance, according to the study, which reviewed 16 years of U.S. Coast Guard data and ship aberrancy rates from the American Association of State Highway and Transportation Officials.

A large ship colliding with a bridge won't necessarily cause collapse, but Shields said it would almost certaintly cause irreperarable damage.

The frequency of ship traffic and how close to the piers they sail were strong predictors of collisions, the study said.

Lousiana's Huey P. Long Bridge, California's San Francisco-Oakland Bay Brdige and Louisiana's Crescent City Connection, Texas's Beltway 8 Bridge and Louisiana's Hale Boggs Memorial Bridge are likely to be hit with ships within less than 40 years, the study said.

"We want that number to be thousands of years," Shields said. “If one of these massive ships hits a bridge, it’s catastrophic."

The Huey P. Long Bridge had the highest risk, with one collision expected every 17 years.

On the other hand, the study said the John A. Blatnik Bridge in Minnesota and Wisconsin should expect a collision within 634 years.

John Hopkins said some bridges with considerable traffic from large ships didn't make the list because their piers are safely on land, away from the passing ships, including Minnesota’s Deluth Lift Bridge and California's Vincent Thomas Bridge.

To prevent collisions, ship traffic should be kept away from piers and piers shoould be equipped with protections including dolphins and other structures.

Still, Shields said there are limits to the predictions.

“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.”