A tractor is the power unit of a tractor-trailer combination. The tractor has the engine and crew compartments and is detachable from the trailer. All tractors have a steering axle and they may have one or two drive axles depending on the weight being hauled. Smaller local tractors or day cabs, typically have just a front row of seating, but some may have an extra row. Long distance tractors have much larger crew areas with a bunk. Some have entire camper set ups with bunks, kitchens, chairs and bath facilities.