Abstract: A semitrailer is described which is capable of conversion between a general freight carrying mode, and an automobile carrying mode. The floor of the semitrailer, which forms a lower tier, is fabricated in a discontinuous shape comprising from the rear end to the front end of the semitrailer an angled section, a drop section, and a horizontal section, the angled section extending downward at an angle whose vertex is located at the rear end of the semitrailer. An upper tier is formed by track supporting members mounted on each sidewall of the trailer which can be pivoted downward from a storage position adjacent to the sidewall, to a horizontal position where the components of the members are connected to form a continuous supporting structure.In the automobile carrying mode the track supporting members are deployed in their horizontal position, thereby permitting automobiles to be placed thereon in an upper storage tier.