Engineer explains difference between Baltimore Key Bridge, Tobin Bridge in Boston

BOSTON - The bridge collapse in Baltimore has local transportation agencies, maritime professionals, and engineers questioning what went wrong.

Dr. Erin Bell is the head of the University of New Hampshire's Civil & Environmental Engineering Department and said the Francis Scott Key Bridge was built with a through truss design. Something she said was evident when nearly all of the bridge collapsed after it had been hit by the cargo ship.

Compare that to the design of the Tobin Bridge in Boston. Bell said that bridge has a cantilever truss which can disperse shock waves and could cause just a section of a bridge to break instead of the entire structure.

"So, if you lose one side you don't lose the whole thing," Bell said. "This bridge (in Baltimore), because it was a through truss, that doesn't happen, which is what we saw this morning and in those videos. I think this will be one of the examples that the bridge community learns from."

During a press conference Tuesday, MassDOT leaders said the Tobin and Braga Bridges were the two under the state's jurisdiction that had pillars in the water with cargo ships that run under them. However, Highway Administrator Jonathan Gulliver said Boston rarely sees a ship as big as the one involved in the tragedy in Baltimore.

"We don't see very many that size coming into Massachusetts and certainly not traveling under our bridges," said Gulliver. "This is going to be a long process to determine what exactly went wrong in Baltimore and we are going to monitoring it very, very closely."