DISCOVERY BAY -- Highway 4 was closed in both directions at the Old River Bridge on Monday afternoon because of a mechanical malfunction, officials said.

The bridge, which carries Highway 4 commuters over the Old River between Contra Costa and San Joaquin counties, was closed about 2:45 p.m., and reopened at 5:08 p.m., authorities said. While the bridge reopened about four hours ahead of CalTrans' initial 9:30 p.m. estimate, residual delays were reported throughout the evening.