A vehicle has a bed of open frame construction, divided into a plurality of bays by means of dividers. Article carriers are constructed to be positioned in the bays by means of a loader-unloader such as a lift truck. Each article carrier may be provided with at least one locking mechanism which automatically unlocks when engaged by a loader-unloader, and automatically locks into the bed of a truck when released by the loader-unloader after being positioned in a chosen bay. The article carriers may be pallets respectively having upper plates which are coplanar and define the entire floor of the bed. The open frame construction of the bed may consist of beams at two different levels, and the pallets may have spaced-apart surfaces resting on the beams respectively at the first and second levels.