The tractor only provides a pulling force and does not bear weight. That is, a full trailer is added behind the ordinary car, and the two are connected by a hook. The trailer can increase the loading capacity of the truck and reduce fuel consumption, thereby reducing transportation costs. The load of the trailer is fully borne by itself, and it is only connected to the locomotive with a hook.http://www.tongyatrailer.com/truck-trailer-semi-trailer/flat-bed-semi-trailer/