(4) "Semitrailer" means a detachable load-carrying unit designed to be attached to a coupling on the rear of a truck tractor by which it is partly supported.

"Semitrailer" means every vehicle with or without motive power, other than a pole trailer, designed for carrying persons or property and for being drawn by a motor vehicle and so constructed that some part of its weight and that of its load rests upon or is [...]