This system of haulage is used for hauling loaded trains of tubs or cars up, or lowering them down, a comparatively steep gradient that is not steep enough, in the latter case, for 1892 a self-acting incline. In the normal system, a single track only is required. The electrically driven or compressed-air-driven engine has a single drum that runs loose on the forged-steel drum shaft; it is controlled by the brake when lowering the empty train, and is clutched to the shaft by means of a dog clutch when hauling the loaded train up the gradient.