As in a regular road vehicle, the tractor unit is steered through the front wheels by a steering wheel operated by a human driver, and powered by its rear single or double axle. The following carriages are then steered through the drawbar couplings between the carriages. Simple trains with few carriages or short in overall length may feature single- or double-axle carriages with just front-axle steering only. Larger or longer trains feature four-wheel steering by way of mechanical linkages. Four-wheel steering ensures that longer trains need less side clearance while turning, as the carriages are able to maintain the same path, describing a constant radius of arc. This adds to the impression of the vehicle being on rails. The drawbar connections of more complex trains may feature a shock absorber to mitigate the effect of acceleration or braking.