PHILADELPHIA — Almost a year after the Francis Scott Key Bridge in Baltimore collapsed as a container ship slammed into it, the National Transportation Safety Board is urging the owners of 68 major bridges in 19 states to assess their vulnerability to such a disaster — including five in the Philadelphia region.

Among them: the Delaware River Turnpike Bridge linking the New Jersey and Pennsylvania toll roads, built in 1956. It is classified as essential to the transportation network and is owned by the two states’ turnpike authorities.

Four bridges owned by the Delaware River Port Authority also made the NTSB’s warning list: the Commodore Barry, Walt Whitman, Benjamin Franklin, and Betsy Ross spans.

The Key Bridge was highly vulnerable to a direct hit from an oceangoing vessel, and the Maryland Transportation Authority had never done an analysis of the risk of a catastrophic collapse, the NTSB said.

“Had they done that, the collapse could have been prevented,” Jennifer Homendy, chairperson of the safety board, said Thursday during a media briefing to announce the recommendation.

NTSB conducted its own analysis of the Key Bridge’s vulnerability, finding its risk level was about 30 times higher than current national engineering standards. The 68 bridges recommended for review were designed before those guidelines, though some have added protective barriers.

The Delaware River Port Authority says each of its four bistate bridges has features to protect the piers, the reinforced concrete pillars that extend into the water and support the superstructure of a bridge while distributing loads to footings anchored in the riverbed.

“Our bridges are very safe, considering the type of shipping channel we’re in and the protections we have in place,” John T. Hanson, the agency’s CEO, previously told The Inquirer.

The Betsy Ross Bridge, like Baltimore’s Key, is a continuous truss bridge, which means it has more piers than a suspension bridge does. But the shipping channel is much less busy at that point on the Delaware River than at the mouth of Baltimore Harbor. And the ships that travel there are smaller.

And the Betsy Ross is protected by “dolphins,” massive reinforced concrete cylinders that protrude above the waterline and are meant to stop ships in the channel from hitting one of the piers holding up the bridge.

DRPA built artificial islands of rocks around the piers of the Commodore Barry Bridge in 2008 to stop a wayward ship from hitting the structure. It said it is reviewing whether more protection is needed for the Ben Franklin and Walt Whitman Bridges.