That group also includes Boston’s Tobin Bridge and the Sagamore and Bourne bridges on Cape Cod. The NTSB said its report “does not suggest that the 68 bridges are certain to collapse,” however.

Maps were also shown that illustrated potential 100-year floods—a flood with a 1% chance of happening in any given year—that could bring pathways under the Tobin Bridge by 2050 and pathways into the ...