BALTIMORE: The Francis Scott Key Bridge, named after the poet who penned the lyrics to the United States national anthem, used to carry around 34,000 paying vehicles a day across one of the busiest harbours in the country.

Its nighttime collapse, within seconds of being struck by a container ship, is likely to cause substantial economic damage for as long as it continues to block shipping in the Port of Baltimore.

The bridge's dramatic destruction shut the port for all maritime traffic, which last year accounted for more than 52 million tonnes of foreign cargo, worth some US$80 billion, according to a recent statement from Maryland Governor Wes Moore's office.

Baltimore is the deepest harbor in Maryland's Chesapeake Bay, and handles the highest volume of autos and light trucks in the US, as well as the largest quantities of imported sugar and gypsum.

The Port of Baltimore is the ninth-busiest major US port in terms of both foreign cargo handled and foreign cargo value, and is directly responsible for more than 15,000 jobs while supporting almost 140,000 more.

It generates around US$3.3 billion in total personal income each year, according to the Maryland State Archives, and brings in almost US$400 million in annual tax revenues.

More than 50 ocean carriers use the port every year, making a total of almost 1,800 trips annually.

Alongside its use as a major port for so-called roll on/roll off container shipping, the Port of Baltimore also serves as a cruise terminal.

Last year, more than 440,000 individuals cruised out of the port - the most since 2012, according to the Governor's Office.

The extended closure of the Francis Scott Key Bridge "will inevitably disrupt commercial activities and supply chains", the Maryland Chamber of Commerce said in a statement.

"Understanding the monumental task ahead to recover from this tragedy and restore this vital transportation link, we urge all residents and businesses to exercise patience and make the necessary long-term adjustments to their daily routines, travel and operations," they added.

Major bridges over shipping lanes like this one are supposed to be designed in such a way to minimise damage in the event of a collision, according to bridge designer Robert Benaim.

"Clearly the protection of the piers in this instance was inadequate," he said.

"A pier or column of a bridge could never resist the impact of a large ship. They must be protected from collision," he added.

"It's evident that the pier couldn't withstand the impact energy, leading to its failure and subsequent collapse of the steel truss and reinforced concrete deck superstructure," said University of Warwick structural engineering professor Toby Mottram.

"The extent of the damage to the bridge superstructure appears disproportionate to the cause, a matter for future investigation," he added.

 - AFP