Carpooling (also known as car-sharing, ride-sharing, lift-sharing and covoiturage), is the shared use of a car by the driver and one or more passengers, usually for commuting. Carpooling arrangements and schemes involve varying degrees of formality and regularity. Formal carpool projects have been around in a structured form since the mid-1970s.
Carpoolers use pool member's private cars, or a jointly hired vehicle, for private shared journeys. The vehicle is not used in a general public transport capacity such as in car sharing, share taxis or taxicabs. Carpooling is also distinct from the use of a company/government or private vehicle by several pool members but at different times, for economic or other reasons, such as in a military motor pool, but might involve single occupancy.
Carpooling reduces the costs involved in repetitive or long distance driving by sharing cars, sharing rental charges, or paying the main car owner. Some countries have introduced high-occupancy vehicle (HOV) lanes to encourage carpooling and use of public transport, to combat rising traffic congestion. In wartime, carpooling was encouraged to save oil. In reducing the number of cars on the road, carpooling decreases pollution and the need for parking space, and in a global perspective, reduces greenhouse gas emissions. Shared driving carpooling can also reduce driving stress. A form of ad-hoc carpooling between strangers is called Slugging. No money changes hands, but a mutual benefit still exists between the driver and passenger(s) making the practice worthwhile.
In some cases, companies or local authorities will introduce facilities to encourage private carpooling, often as part of wider transport programs. These can include central listing facilities, defined pick-up points, preferential parking and general advice. This has increased through use of the Internet, mobile phones and other software support systems. A third party rideshare agency may also provide services to enable one off or regular carpooling in defined areas. In the "dynamic ridesharing" concept, a separate system performs a carpool match automatically for approval by the travelers.
Inflexibility in carpooling can arise in accommodating en-route stops or changes to working times/patterns. Some larger carpools offer 'sweeper services' with later running options. A further backup can also be a 'guaranteed ride home' arrangement with a local taxi company.