Another practical solution would consist of avoiding the low occupancy of most vehicles in cities, through car sharing, so that empty seats are used in most trips. This modality is known by the term carpooling and has been proposed as an effective way to reduce pollution and cut expenses. A related but different approach, known as carsharing, is based on collective fleets of cars that can be temporally rented by multiple users, but such a solution does not solve the aforementioned problem because it does not imply that users share the vehicle at the same moment. There is another term, ridesharing, which is generally used to refer to different solutions to share the use of a car with other people in order to travel to a particular destination. In addition to carsharing and carpooling (also known as real-time or instant or dynamic or ad hoc ridesharing), ridesharing also includes other versions known as slugging, lift sharing and covoiturage. This work does not address ridesharing solutions different from carpooling.