Reallocation of Empty Personal Rapid Transit Vehicles en Route

Abstract

Personal rapid transit (PRT) accommodates groups of passengers that request transport to a desired destination. Empty vehicles need to be moved to stations with waiting passengers or with expected demand. Efficient redistribution of empty vehicles is critical in larger PRT networks, which have running times longer than acceptable waiting times. Previous studies have developed methods for allocating destinations to empty PRT vehicles sequentially as they become available. This study refines the allocation of empty vehicles into three stages. The first stage is essentially the previous sequential allocation. In the second and third stages, empty vehicles en route are reallocated by switching destinations. In the second stage, waiting passengers are allocated the nearest vehicle on the basis of waiting time. In the third stage, the remaining empty vehicles en route are reallocated on the basis of minimum running distance. The optimization problem in the third stage corresponds to the transportation problem, and it is solved approximately by a heuristic method suggested by Russel. Applied to a network with 25 stations, 16 km of guideway, and 200 vehicles, the combined reallocation methods reduced average waiting and the longest wait to about half compared with sequential decisions alone.