High occupancy vehicle

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. 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. 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. Because it's less crowded, an HOV lane can move at full speed even in traffic jams. Therefore, during a traffic jam on a ten-lane highway (five lanes each direction, one each direction an HOV lane) each vehicle in the HOV lane moves at least two people, four to ten times as fast as the people in single occupancy vehicles. In theory, an HOV lane could move five times as many people as the rest of the freeway combined under these circumstances. 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 a 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.

See also car pooling in the automobile article.