Authorities are searching for the driver of a truck that went off a highway bridge and into a Buchanan County river Friday afternoon (July 21, 2017).

The accident happened on U.S. Highway 20 between Independence and Winthrop, but the exact time hasn't been determined. Road maintenance workers discovered the mishap around noon when they noticed a damaged guardrail on a bridge spanning the Wapsipinicon River.

According to the Iowa State Patrol, a straight truck was travelling westbound on the U.S. 20 when it left the highway, entered the median and collided with the guardrail. Troopers said the vehicle then vaulted off the bridge embankment and plunged into the river.

The crash forced the closure of westbound U.S. 20 for several hours, while cranes pulled the cargo truck from the water.

The accident remains under investigation and the search for the driver continues.