Shared mobility systems are increasingly deployed in cities around the world. Such systems allow users to rent a vehicle for a short period and return it in any of the system's stations scattered throughout the city. There are many advantages to shared mobility systems. Among others, they reduce city traffic congestion and improve utilization of city land resources, as the need for parking spaces is decreased. For most users, the sharing of resources typically results in lower costs as compared to owning a private vehicle. In addition, users are not troubled about securing the vehicle when not in use and are not troubled about repairs.
The main challenge of shared mobility system operators is to satisfy demands for vehicles (on rent) and for vacant parking spaces (on return). The demands are typically stochastic, non-stationary and asymmetric processes. Occasionally, users may find that some stations are empty (no available vehicles) and some are full (no available parking spaces). In this study we measure the performance of the system by the total excess time spent by users due to unfulfilled requests for vehicles or parking spaces.
For the first time, we propose using reservation policies in shared-mobility systems and examine their effect on the system's performance. In particular, we focus on reservations of the parking spaces. In this study we investigate a policy which we refer to as the Complete-Parking-Reservation (CPR) policy. According to this policy, when a user rents a vehicle he declares his destination station and a vacant parking space in that station is reserved for him, if one is available. This assures that when the user reaches his destination he will be able to return his vehicle. If there is no available parking at the destination the transaction is denied and the user can either abandon the system or try to reserve a parking space in a different station.
The CPR policy is compared to the base policy, entitled No-Reservation (NR) policy. We prove that there always exist conditions for which a CPR policy performs better than an NR policy. Furthermore, we show that the CPR policy outperforms the NR policy in a substantial part of the range of conditions in which a system can actually be operated. This is demonstrated by analytical analysis of Markovian models of small systems. In addition, this result is verified via an extensive simulation study of large realistic systems.
