of rail engaging wheels mounted to its underside a first set of wheels 122a 122b mentioned earlier engages longitudinal parking rails 63a 63b also see fig2 and a second set of wheels 124a 124b disposed normal to said first set engages transverse central rail 106a the first set of wheels is normally elevated with respect to the second set and engages the longitudinal rails that define the parking spaces when lowered in other words the second set of wheels has an extended configuration and a retracted configuration see the phantom lines in fig6 and are in said extended configuration when carrier 72 shuttles along central rails 106a 106b thus the first set of wheels 122a 122b is held above the longitudinal rails 63a 63b to allow such transverse movement of said carrier upon arriving at a parking space said second set of wheels 124a 124b is retracted thereby lowering wheels 122a 122b onto longitudinal tracks 63a 63b as depicted in fig6 carrier 72 can then enter the parking space retract its pallet supporting pins so that the pallet is supported by support posts not shown in fig6 and withdraw from beneath the pallet and return to central rail 106a 106b upon extension of the second set of wheels an individually assigned parking space may be found by the carrier by many differing means such as physical pin coding laser coding and the like all of which means are within the scope of this invention for example each parking space could be bar coded and each carrier could carry a scanning means connected to the central computer similarly each pallet would be.