An unmanned barge drifted out of control and struck a highway bridge over the Severn River near Annapolis on Tuesday.

Police had stopped traffic from crossing the U.S. 50 bridge after the barge was reported adrift in the river, and the roadway was empty when the barge hit two bridge pilings and wedged against them.

It wasn't immediately clear how the barge got loose or if the bridge, a major thoroughfare leading to the state capital and the Naval Academy, was structurally damaged. Coast Guard investigators and the barge owner were headed to the area Tuesday, official said.

Coast Guard spokesman Lt. Andrew Ely said the barge belongs to Langenfelder Marine Inc. of Stevensville and was hauling rock.