March 26, 2024

Thoughts on the Key Bridge Collapse

I awoke this morning to the news that the main span of Baltimore’s Francis Scott Key Bridge was struck by a container ship and plunged into the Patapsco River. Dramatic video was already on the Web showing the accident. The ship, the Dali, apparently experienced a power failure and drifted into the south pier of the central span. Unsurprisingly, a collapse followed immediately. Apparently, the ship sent out a mayday message, and police were able to divert traffic before the I-695 bridge was hit. News reports this afternoon were raising questions about the bridge design.

The span in question was a continuous truss opened in 1977. There is no indication that the bridge was in any way defective.  It is difficult to imagine any that 1200-foot long bridge could survive a significant strike of a main support. Since the bridge was built, cargo ships have gotten much larger. The Dali is nearly a thousand feet long. Such a ship, even at low speed, carries enormous momentum. The bridge could perhaps have been protected by a fender or wall to protect the main piers. But any such protective obstacle would need to be massive indeed given the size of current cargo ships.

The immediate question is what a replacement for the bridge should look like. One attractive alternative would be replacing the bridge with a tunnel. This would be an expensive, time-consuming, and disruptive option. I suspect a new bridge will be built instead. Although the main span of the Key Bridge was a continuous truss, its approaches were carried by a series of simple beam bridges built into the river. The most obvious and secure way to protect a new bridge from out-of-control vessels is to increase the span of the bridge, perhaps even putting its piers on dry land. This would require that the much longer bridge would need to be a suspension bridge. Not only would such a bridge be better protected from accidental damage but also it would allow for construction with hardly any negative impact on traffic in what is a vital shipping channel.

Today, I heard replacement of the Francis Scott Key bridge compared to the rapid bridge replacements effected recently in Pittsburgh and Philadelphia. Such comparisons are absurd. The task faced in Baltimore is enormous and will, in any case, take years.

We will have to wait to see what sort of replacement roadway is ultimately chosen. Neither a cheap nor a fast replacement is possible.

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