At least two coal-filled barges have sunk and about a dozen others have been corralled after they broke loose on a river in western Pennsylvania, colliding with bridges as they floated freely downstream.

The runaway barges were spotted Thursday on the Monongahela (muh-nahn-guh-HAYL'-uh) River outside Pittsburgh. Traffic was shut down for hours on two bridges spanning the river after the barges hit one of them and started drifting toward the other. A railroad bridge was also struck. Crews are inspecting the bridges that were hit.

Tugboats and other vessels were called in to secure the barges.

The state Department of Environmental Protection says any coal that went into the river is unlikely to cause a threat downstream.