 As the tractor reverses under the trailer, a kingpin under the front of the trailer slides into a slot in the skid plate, and the jaws of the fifth wheel close onto it.The driver has to raise the trailer legs manually, and couple the airbrake lines and electrical cables.Some low-set trailers such as lowboys/low-loaders and car transporters have electrically-powered landing gear due to the necessarily low clearance prohibiting conventional landing gear.