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As officials continue to investigate the collapse of Baltimore’s Francis Scott Key Bridge, experts say it is unlikely any bridge could have withstood the impact of a vessel as large as the Dali cargo ship. But better detection and warning systems could have potentially helped mitigate the disaster.
“While it was shocking to see something made of steel and concrete come down so quickly, it wasn’t really surprising given the size of the vessel in comparison to the bridge piers,” said Rachel Sangree, an associate teaching professor in Johns Hopkins University’s Department of Civil and Systems Engineering.
Benjamin W. Schafer, a structural engineer and professor of civil and systems engineering at Johns Hopkins, said the Key Bridge did have some protection at the bottom of the bridge, as evidenced by the pier that’s still standing. But that wasn’t enough to ward against the 984-foot ship.
“It’s pretty modest,” Schafer said, referring to the pier protections. “It’s not even at the bow line. The ship was much higher than that protection, so it wouldn’t really make any stop for a cargo ship. Something like a small fishing vessel or a pleasure cruise wouldn’t be able to hit the piers directly, but no significant system directly at the piers.”
Could any system be practically designed to hold up to a hit from a vessel this large?
“There’s little evidence that it’s economically feasible to create a protection system for a cargo ship that is coming at a full straight-on blow,” Schafer said. “So the need for the protection system is to have diverted the ship … far enough away from the pier itself that a lot of that energy could be dissipated before it’s directly impacting the pier.”
He added, “Could we build a Fort Knox, a nuclear bunker in front of every bridge? It’s structurally possible, but it’s not economically feasible. And so even in the most extreme bridge protection systems that we see, at this point I remain unconvinced that in a similar incident that they would perform successfully.”
Although additional structural protections may not have held up to the Dali, a better early warning system could have helped prevent the crash, said Susu Xu, an assistant professor in the Department of Civil and Systems Engineering at Johns Hopkins.
When the Dali lost power, the ship’s pilots sent out a mayday call to alert authorities about their power issue. That call allowed transportation officials to stop additional vehicles from driving onto the bridge, averting further loss of life.
Xu hopes the investigations will reveal whether and how the bridge’s defender systems need to be reinforced, as well as how to ensure systems alert people to evacuate in a timely manner.
There should be sensors on the piers or on the bridge deck that can detect when the ship is getting close, Xu said. If a ship loses control, the sensors could automatically issue warnings to agencies, who would then alert the bridge about the possible collision.
“In the meantime, once they are activated by the collision detection, they should immediately flash and send alarms on the bridge and also change the traffic signals to stop the traffic onto the bridge so that people can be evacuated and nobody can get on the bridge anymore,” Xu said.
While the rebuild will include physical changes, Schafer said, the social and maritime changes will also be key to creating a successful system that avoids another bridge strike.
Schafer said he has heard suggestions that another tunnel should be built instead of a new Key Bridge. That option is unlikely, he said, because hazardous materials cannot be transported through tunnels.
“The only way you can get them around Baltimore now is to go over the former Key Bridge,” he said. “They’re not allowed in the tunnels. So my expectation is we will rebuild a bridge, but will it be in the exact same place and form and everything? It’ll be an open question of what we’re trying to do.”
Draw bridges and lift bridges could also span the channel, but even those types of structures will need to have piers in the waterway, Sangree said.
She added that the new bridge will need to be big enough to not only allow for the sizes of ships today, but also potential future growth in ship sizes.
“The Key Bridge was very, very tall,” she said. “But whatever is selected, it will of course have to accommodate not only the existing sizes of the shipping vessels, but any thoughts of larger sizes. Because we don’t want to design exactly for what we’re seeing right now but always be thinking ahead.”
Regardless of what the new bridge looks like, Sangree said officials will learn from the Key Bridge collapse and apply that knowledge to build safer and more effective systems.
“Unfortunately, these sorts of tragedies often do result in better understanding of how to move forward in designing our infrastructure systems,” she said. “They’re also reminders of the importance of continuous investment in our infrastructure systems. Not just in the bridge itself, but this is a complex and interconnected couple of systems that are coming together under this bridge between the port and the surface transportation network itself.”
