Authorities in Minnesota said no one was hurt when a 1,200-pound chunk of concrete tumbled onto highway traffic.
They said the slab tore off the underside of an overpass in St. Paul over the weekend. The 6-foot-by-9-foot section fell onto two vehicles.
More than eight hours of gridlock followed along Interstate 35E as crews inspected the overpass, which shuttles nearly 140,000 motorists a day through downtown St. Paul. Authorities say the 50-year-old bridge is "structurally safe."
The incident comes nearly a year after the deadly collapse of a Mississippi River bridge in neighboring Minneapolis. The St. Paul bridge isn't scheduled to be replaced until 2014.