Concrete structures meant to protect Baltimore bridge appear unchanged for decades

Seconds before the container ship Dali hit the Francis Scott Key Bridge in Baltimore last week and tore it down, killing six construction workers, it sailed past a structure designed to prevent that kind of disaster.

Those structures — known as dolphins — are circular concrete constructions located near a bridge's central supports. Vessels are meant to crash into them if they veer off track in the shipping channel, diverting them from collision with the bridge. Four such dolphins remain intact in the Patapsco River. The one the Dali narrowly missed is located on the right side of the ship, and is dwarfed in size by the vessel which appears to be more than 15 times as long.

Experts said if the Baltimore bridge had been outfitted with more robust collision-prevention structures, it may not have been struck. Although Maryland has invested in repairing the Key Bridge, records reviewed by NPR indicate the dolphins have not been substantially changed since they were built in the 1970s.

A more robust protection system would have given the Dali a better chance of hitting the dolphins before the vessel collided with the bridge, said Roberto Leon, a professor of structural engineering at Virginia Tech.

"They were very, very small," said Leon. "You needed more, and bigger ones, is really the point."

When the Key Bridge was opened in 1977, cargo ships sailing through the Port of Baltimore were smaller and lighter than modern ones. The dolphins, which were added shortly after the bridge was finished, have saved the structure at least once. In 1980, a ship crashed into one dolphin, destroying it but sparing the bridge.

Since then, the sizes of cargo ships have ballooned. They can now carry about 10 times more weight and extend almost two times as long as when the Key Bridge and its dolphins were designed. The American Association of State Highway and Transportation Officials, the organization that sets standards for bridge construction safety, requires newer bridges to build robust collision prevention structures. Many ports have them.

Satellite imagery of bridges critical to 15 of the busiest U.S. ports indicates there are few bridges like the Key Bridge that lack immediate protection for their main support piers. The bridges' central supports are more often protected by fenders, islands of rocks, concrete beds or land — the use of remotely located dolphins or no protection at all is less common.

But the transportation rules don't strictly require that collision-protection structures built with older bridges be fortified or replaced. Instead, in 1991, the American Association of State Highway and Transportation Officials set guidelines for assessing bridges to determine whether or not they should be updated.

Some conducted those analyses. John Hanson, the CEO of the Delaware River Port Authority, the group that stewards four bridges that cross the Delaware River between Pennsylvania and New Jersey, said they completed a vulnerability assessment in 2003 and determined that updates were not needed for the Betsy Ross Bridge's dolphins in Philadelphia. Among the bridges of the 15 busiest ports, the Betsy Ross was the most similar in structure to the Key Bridge, and one of the only ones that also uses dolphins to protect it.

Even so, satellite imagery shows the dolphins constructed around the Betsy Ross Bridge appear more robust than the ones surrounding the now collapsed bridge in Baltimore, said Kim Roddis, a structural engineer and professor at George Washington University.

"It's definitely more protective," said Roddis. "One of those is really quite large."

NPR asked the Maryland Transportation Authority whether a threat assessment had been conducted for the Key Bridge and whether the agency had invested in enhancing the dolphins' structures since they were built in the 70s. The agency did not respond.

Every year, the Maryland Department of Transportation conducts a report that evaluates the state's transportation infrastructure and determines its priorities for investment. Repairs to the bridge were suggested in 2017, that year's annual report states, and satellite imagery indicates two transmission towers were constructed between 2019 and 2022, on the side of the bridge closer to Baltimore city. But nautical charts show the current sizes of the dolphins are similar to their original 1978 dimensions — the four don't appear to have been significantly enlarged since then.

Leon, the professor of structural engineering at Virginia Tech, said states face tough choices when it comes to spending on infrastructure.

"They have lacked resources for many years," he said. "And so they tend to take care of what they think are the more urgent problems."

But putting off this kind of investment can have dangerous consequences, he said.

"Unfortunately, we have taken things for granted for too long. We haven't done the appropriate maintenance, the appropriate upgrading," remarked Leon. "And so this is the result of that."

Copyright 2024 NPR. To see more, visit https://www.npr.org.