Cooper said there were four passengers on the bus at the time, and they all knew something was wrong when the driver made the turn. He said the wheels locked up and there was nothing the driver could do.
"She was riding the wheel, just hoping we stopped," Cooper said.
Emergency dispatchers said paramedics evaluated people at the scene. Port Authority of Allegheny County spokesman Jim Ritchie said one person who was in a car suffered a minor injury.
The Port Authority is investigating the crash.