A dynamic clustering method for relocation process in free-floating vehicle sharing systems

Recently, vehicle sharing emerged as a new type of mobility service. In particular, if these systems happen to be free-floating, their operating area is typically located within the city and vehicles could be picked-up and parked in any permitted spot, and not only at predetermined stations. This specific feature enables everyone to pick-up and drop-off a rented vehicle close to his demand points, with no need to visit a station before or after the ride, granting greater flexibility for users together with the opportunity of a shorter trip. Free-floating systems, due to their inherent characteristics, are becoming more popular; however, at the same time, they involve additional operational challenges especially in facing the relocation processes, namely displacing vehicles from areas with higher concentration toward those with a higher request of the service. Similar to the station based ones, free-floating vehicle shared-use systems deal with significant fluctuations in demand, depending on day/time and area of a city. Therefore, we suggest a methodology for generating a dynamic zone clustering in order to define cost-efficient relocation strategies. The aim of the proposed flexible clusterization is identifying the optimal size and number of areas among which perform an effective and enhanced vehicle repositioning, reducing the necessity to move vehicles from one zone to another and, accordingly, shrinking the relocation costs. The proposed method is applied to a test case study, in order to verify the accuracy of the suggested model.