Some of the nation’s most prominent bridges are susceptible to ship collision and collapse similar to the Francis Scott Key Bridge disaster that occurred a year ago.
A new study from Johns Hopkins University found that the Key Bridge collapse was not a rare occurrence and some of the busiest bridges in the United States could collapse within the next few decades.
“The major finding is that the collision risk for us bridges is very significant, and that we've underestimated it,” said Michael Shields, an associate professor at the Johns Hopkins School of Engineering and co-author of the study. “If individual bridges are expected to see collision events every few decades, then that means that across the nation, we should expect collision events to occur every few years, every three to five years, and actually, historically, that's what we've seen. This is entirely consistent with historical precedent.”
The study outlines the bridges most at risk within the United States and estimates how often they can expect a collision.
Louisiana’s Huey P. Long Bridge ranks highest with a collision expected every 17 years.
The San Francisco-Oakland Bridge can expect one every 22 years and another Louisiana Bridge called the Crescent City Connection ranks third with a possible collision every 34 years.
Maryland’s Chesapeake Bay Bridge ranks twelfth with the potential for an accident every 86 years.
The researchers came to the conclusions by using sixteen years worth of U.S. Coast Guard data including ship locations, speed and location points and then cross referenced that information with port and bridge data.
Shields says many older bridges were built before industry standards were put in place for collisions.
“Bridges like the Chesapeake Bay Bridge, like the San Francisco Oakland Bay Bridge, like the Key Bridge, were not designed with any provision for ship collision in their design,” Shields said. “While the new bridges are required to have to be designed according to those provisions. There's been no mandatory effort to retrofit existing bridges to make them compliant with those standards.”
The American Association of State Highway and Transportation Officials set assessment recommendations in the early 1990s.
Stephen Flynn, a critical infrastructure analyst for Northeastern University’s Global Resilience Institute, says there are a handful of options to protect bridges for a fraction of the price of a disaster like the Key Bridge.
“It’s not rocket science,” Flynn said. “The basic safeguards are you build essentially a mini-Island around the support column that ideally, if a ship got even close to it would run aground on the island instead of on, instead of hitting the support column, but you also put out things called dolphins. These are almost like bumpers on a pinball machine.”
Last week, the National Transportation Safety Board put out recommendations to try to remedy some of the issues.
The NTSB is issuing urgent recommendations to 30 bridge owners in 19 states that 68 bridges need to be assessed for vulnerabilities because they were not built and designed to AASHTO specifications. “They need to determine what their risk is and start to put in those protective measures if warranted,” NTSB Chair Jennifer Homendy said. “There is a safety deficiency here, a potential safety risk, and you need to take immediate action. We will follow up with all of the bridge owners.”
The NTSB concluded that Maryland’s transportation authority failed to assess the Francis Scott Key Bridge for threats for decades, leaving the bridge 30 times more vulnerable than thresholds set by industry standards.
“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. “What's frustrating is, not only did MDTA fail to conduct the vulnerability assessment on the Key Bridge, they did not provide, nor were they able to provide, the NTSB with the data needed to conduct the assessment, including the characteristics of vessel traffic passing under the bridge, vessel transit speeds, vessel loading characteristics.”
