Car-pool lane
A high occupancy vehicle (or HOV) is any vehicle with a driver and one or more (or sometimes two or more, or three or more) passengers. When an automobile is used as an HOV, it is often called a carpool, though the term HOV includes buses and vans. An HOV may be allowed to travel on special road lanes, usually denoted with a diamond marking in the United States, on which single occupant vehicles are prohibited. In some areas, such as Southern California, the HOV lanes are full-time, while in others, such as the San Francisco Bay Area, they are usable by other vehicles outside of peak hours. The term is used in transportation engineering and transportation planning.
The relative rarity of high occupancy vehicles to single occupancy vehicles in the United States make HOV lanes work. When it is uncongested, an HOV lane can move at full speed even when parallel (non-HOV) lanes suffer delays from queueing at bottlenecks. In theory (and often in practice), an HOV lane moves more people per lane at a higher speed while moving fewer vehicles. In practice, however, the proximity of a slowly moving lane adjacent to the HOV lane and occasional merging slows HOV traffic. Multiple or separated HOV lanes can be used to address these issues.
Proponents of HOV lanes say that this is a good return on the laws, paint and signs that an HOV lane requires. Additionally, a single engine carrying multiple passengers uses less fuel per trip, saving money and creating less carbon dioxide and noxious pollutants than if each passenger drove their own car.
Opponents say that at the critical point when heavy traffic is about to become a traffic jam, the loss of the HOV lane from general use actually precipitates the traffic jam, making its usefulness a hollow victory. They also question how much ride-sharing they actually encourage, instead of merely advantaging those who would be sharing a vehicle anyway. HOV lanes added to existing highways also create more congestion at exits and interchanges because often no HOV-only exits are provided; the normal central position of the HOV lanes means that vehicles must transition across all lanes of traffic in a short distance to exit.
Because HOV lanes seldom maximize vehicle throughput, a number of cities are considering converting under-utilized HOV lanes to High occupancy-toll lanes (Or HOT lanes). This would permit single occupant vehicles to buy the right to use the HOV lanes for a toll, but total flow would be regulated (the price would be varied) to ensure total speeds on the HOV lane do not drop noticeably.
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