The Key Bridge was knocked down after the cargo ship Dali lost power and smashed into a support pier, killing six road workers and partially blocking the shipping channel for months. The calamity illustrated the importance of planning — or at least trying to — for the future; the bridge wasn’t built with 100,000-ton ships in mind and was ill-prepared for vessel strike. It prompted a National Transportation Safety Board investigation into what went wrong and a Coast Guard probe into national port infrastructure.

Rebuilding the Key Bridge with the same, 185-foot clearance would probably suffice for the immediate future. But as public entities along the East Coast spend millions and billions to stretch out their spans and dredge channels deeper to accommodate larger vessels, planning likely will call for a taller bridge.

Big ships, rising tides

There are few things physically stopping container ships themselves — which doubled, then tripled and now have increased ten-fold in capacity since the 1960s — from growing. In fact, there is an economic incentive for them to get bigger.

But external factors could stall their growth. It’s not unlike semitrucks in the U.S. They could be built longer than 53 feet, but external factors (various states’ laws) limit them, said Jean-Paul Rodrigue, a Texas A&M University professor whose research focuses on transportation and logistics.

In the case of cargo ships, it isn’t laws that could restrict their size, but infrastructure. For one thing, there are barriers directly below and above them. Most shipping channels into ports are no deeper than 50 feet, and bridges often set a maximum height.

Capt. Jeffrey Monroe, a master mariner and education director for the International Association of Maritime and Port Executives, said that as ships have grown, “we began to dig deeper.” Baltimore’s channel has been 50 feet deep since the 1970s, but Charleston recently deepened its channel to 52 feet and New York/New Jersey is studying the possibility of dredging to 55 feet.

“Then we began to realize that now our biggest limitation is not the depth of the channel,” said Monroe, who consulted on a project to greatly increase the vertical clearance of the Bayonne Bridge, which connects New Jersey and Staten Island, New York. “Our biggest limitation is the infrastructure that flies over the top of it.”

Aside from channel depths and bridges, there are limitations to international shipping. The narrowness of a vital shipping channel near Singapore, the Malacca Strait, as well as the width of the Panama and Suez canals would complicate efforts to make ships larger.

But there are already ships built today that can’t fit into the Port of Baltimore. And it’s not just bridge height that limits them. Channel dimensions and the “capacities of a container terminal” also determine the size of a ship that a port can handle, said Richard Scher, spokesperson for the Maryland Port Administration.

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