Police say they're investigating what caused a Greyhound bus to leave a highway and plunge through a fence, injuring 17 people in Madison, Wis.

The bus was carrying an estimated 80 passengers when it crashed Friday night on Interstate 39 near the Highway 151 interchange, state police said.

The injured, who were taken to three hospitals, were expected to recover, Madison fire officials told the Wisconsin State Journal in a story published Saturday.

The bus came to rest in a field and was driven back onto the road after ambulances left with the injured, the Journal reported.