A balloon loop, turning loop or reversing loop (North American) allows a rail vehicle or train to reverse direction without having to shunt or even stop. Balloon loops can be useful for passenger trains and unit freight trains such as coal trains. Balloon loops are common on tram or streetcar systems. Many streetcar and tram systems use single-ended vehicles that have doors on only one side and controls at only one end, or they haul trailers with no controls in the rear car and so must be turned at each end of the route.