Relocation-related problems in vehicle sharing systems: A literature review

•Relocation-related problems in car-, bike- and scooter-sharing systems are reviewed.•A hierarchical classification of relocation strategies is proposed.•The similarities and differences between different types of systems are analyzed.•The universal modeling and solving methods are analyzed.•Promising directions in both problems and methodologies are pointed out. With the maturity of vehicle sharing systems including carsharing, bike-sharing, and scooter sharing systems, the imbalance of vehicle distribution across the service area has become a main operational challenge faced by service operators. In recent decades, various relocation strategies have been developed to help operators alleviate the troublesome imbalance. This review proposes a hierarchical classification of relocation strategies and presents a deep survey on relocation-related problems. The relocation strategies at different decision levels are first distinguished and then further classified based on execution modalities of relocation activities. For each relocation strategy, the similarities and differences among different types of systems and universal modeling and solving methods are analyzed; the application states and challenges of practices are also briefly analyzed. Promising research directions in both problems and methodologies are highlighted. It is hoped that this review will be beneficial to the community of relocation-related problems in vehicle sharing systems.