TAMPA, FL (AP) Authorities in Tampa are still trying to determine why part of a road under construction has collapsed, closing the Crosstown Expressway to Brandon.

The problem has snarled traffic and sent two construction workers to the hospital. The Florida Highway Patrol said a concrete column supporting a new elevated span sank 15 to 20 ft. (4.6 to 6 m) into the ground early this morning causing the span to collapse.

No cars were damaged, but the Florida HIghway Patrol was forced to shut down the existing lanes of the expressway. It’s heavily used by commuters from Tampa’s east suburbs.

The two construction workers suffered minor injuries.