Major bridges at high risk of a ship collision capable of causing a collapse, Johns Hopkins study says
A Johns Hopkins University study has found that catastrophic collisions with bridges by massive freighter vessels is all too likely.
Michael Shields, a Johns Hopkins University engineering professor, got an email last March after a supersize container ship hit the Francis Scott Key Bridge and it tumbled into Baltimore Harbor about nine air miles from campus.
What do you think the chances of this actually happening were? a colleague asked.
That moment led to a study by a team of 19 scholars and preliminary findings that confirmed what Shields had told his friend after some quick math: The chances were much higher than expected.
“In retrospect, we should have seen it coming,” said Shields, who specializes in the risk and reliability analysis of engineering systems and structures. “The reality is that ships collide with bridges on a fairly regular basis.”
Johns Hopkins released a ranking on Monday of the 20 most vulnerable bridges in the nation, based on the estimated probability each could be struck by a large ship hard enough to cause catastrophic damage or a collapse.
Among the causes are rapidly increasing shipping traffic and ever-bigger container ships that dwarf anything that sailed under the bridges when they were built. The 984-foot Dali that hit the Key Bridge was about 10 times larger than most oceangoing freighters were when it opened in 1977.
The Key Bridge would have been among the 10 most at-risk bridges in the country, according to the team’s calculations, due for a likely ship strike within 48 years. The bridge was 46 years old when it fell.
By modern engineering standards, the yearly chance of a bridge collapse should be 1 in 10,000, Shields said. Most bridges near ports and the waterways that lead to them were built well before those standards were issued in 1994, and there is no requirement that owners retrofit the spans with protective barriers (though some have done so).
In the Philadelphia region, the Delaware Memorial Bridge has a 1-in-129 annual chance of a direct hit by a ship, the Hopkins researchers found. That sounds like plenty of cushion, but danger is closer than it appears. The bridge ranked No. 15 on the vulnerability list.
But the Delaware River and Bay Authority, which owns and operates that I-95 bridge between New Jersey and Delaware, is spending $19.1 million this year to install a protection system that meets modern standards. Crews are placing eight cylindrical “dolphin” structures, 80 feet in diameter, two at the approach to each tower pier of the twin spans.
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Over the last 50 years there have been a dozen or more ship-bridge collisions in the U.S. Not all were as devastating as the Key Bridge collapse, but the historical record alone suggests a collision capable of serious damage could be expected roughly every three to five years.
“We hope the findings of this study ultimately motivate local, regional, state, and even federal officials to recognize that investment is critical,” Shields said. “If you don’t make the investment, this will happen again, potentially within a decade or less.”
He led the research team, which included engineering professors, a postdoctoral fellow, and both graduate and undergraduate students. They collected and mined 16 years of U.S. Coast Guard data — digital logs detailing the precise location, heading, speed, and status of every ship traveling through the country’s waters, minute by minute.
They cross-referenced that geolocated shipping information — hundreds of millions of data points — with information about the size of ships and bridge specifications from the National Bridge Inventory, compiled by the Federal Highway Administration. The researchers started with bridges with the thickest traffic passing beneath of large ships, defined as those longer than 150 meters (492 feet), and mega ships, those longer than 300 meters (984 feet).
The nation’s most vulnerable span is the Huey P. Long Bridge near New Orleans, built in 1935, which could expect a major ship strike once every 17 years, the study found.
“If I look at the San Francisco-Oakland Bay Bridge, we’re likely to see a major collision once every 22 years,” Shields said. “That is huge. We want that number to be thousands of years. That’s tens of years.”