WILMINGTON, Del. (AP) — A tractor-trailer cab crashed through a concrete barrier Friday and plunged off the Delaware Memorial Bridge into the Delaware River, authorities said. It wasn’t clear how many people were in the cab, which was found in about 20 feet of water, according to the Delaware River Bay and Authority.

Authorities say a bobtail tractor careened off the Delaware Memorial Bridge, plunging into the river below. What is a bobtail truck?