Vehicle relocation problems in free-floating car-sharing systems

Official URL: https://risc01.sabanciuniv.edu/record=b2486364 _(Table of contents)

Car-sharing systems have attracted plenty of attention for the past few decades as a means to fulfill constantly growing mobility needs especially in urban areas, and to alleviate the difficulties caused by economical and environmental problems due to excessive (and increasing) private car ownership. One of the main challenges faced in car-sharing systems is to maintain a good balance between vehicle supply and user demands by means of relocating the vehicles from regions with excess supply to regions with excess demand. We examine two vehicle relocation problems in a free-floating car-sharing system, which allows users to pick up/drop off vehicles from/to any location of their choice, and pay as they go. Vehicle relocations are typically performed by dedicated personnel, also known as operators, in car-sharing systems. First, we propose an operator-based vehicle relocation model which provides a relocation plan for the vehicles along with a set of routes for the operators consistent with the planned relocation tasks. Second, we formulate a hybrid relocation problem where, in addition to operators, users are also encouraged to participate in repositioning of the vehicles in return for a discount. Both problems are formulated as mixed-integer programs on appropriately defined time-space networks. Furthermore, new sets of instances are generated, and the proposed models are used to obtain solutions to these problem instances. A computational study is conducted to evaluate the operational efficiency of the car-sharing system based on key performance indicators, namely, objective value, number of rejected users and vehicle/operator utilization levels.