In transportation engineering and transportation planning, a high-occupancy vehicle lane (or HOV lane) is a lane reserved for vehicles with a driver and one or more passengers. These lanes are also known as carpool lanes, commuter lanes, diamond lanes, express lanes, and transit lanes.
Qualification for HOV status varies by locality, and may require more than two people. When an automobile is used as an HOV, the group of people using it is often called a carpool, though the term HOV includes buses and vans. However, bus lanes may not necessarily be intended for use by carpools. An HOV or carpool may be allowed to travel on special road lanes, usually denoted with a diamond marking in the United States and Canada, on which single occupant vehicles and trucks are prohibited, called restricted lanes, carpool lanes or diamond lanes. In some cases, single occupant vehicles are allowed provided that they are hybrid vehicles or use native fuels. U.S. federal law states that HOV lanes "must allow motorcycles and bicycles to use the HOV facility, unless either or both create a safety hazard. In Canada, no such exemptions exist. In some areas, such as Atlanta, Southern California, Hartford, Connecticut, Seattle Area, Boston Area and the Greater Toronto Area, the HOV lanes are full-time, while in others, such as the San Francisco Bay Area, Phoenix, Long Island, and Northern New Jersey, they are usable by other vehicles outside of peak hours. Honolulu uses a "zipper" barrier to create an additional HOV lane on the westbound side of Interstate H-1 during peak hours.
In some regions, buses are allowed to travel on the road shoulder when traffic becomes heavy, but it is often still illegal for cars (even HOVs) to take the shoulder to get around traffic jams. Highway 403 in Mississauga, Ontario (Near Toronto, ON) and Highway 404 in York Region and Toronto, Ontario, Canada for instance had their shoulders widened in 2003 and 2004 respectively, so they serve a dual purpose as bus lanes and accident lanes. Although full HOV lanes are available for carpooling traffic, buses still continue to use shoulders along the 403. In Columbus, Ohio, shoulders on I-70 are HOV lanes reserved for buses at all times.
In emergency situations, an HOV "cordon" is sometimes placed prohibiting all vehicles from crossing the cordon during specified times. The cordon is enforced through the use of police checkpoints. For example, Midtown and Lower Manhattan were placed under cordons during the morning peak hours in the aftermath of the September 11, 2001 attacks and during the 2005 New York City transit strike.
In practice for some communities, including Atlanta, Houston, Los Angeles, Washington, D.C., and Seattle, HOV lanes regularly carry more people than adjacent regular lanes of travel, as reported by the Transportation Research Board HOV Committee
Various organizations and services make it easier for commuters to utilize HOV lanes. Regional and corporate sponsored vanpools, carpools, and rideshare communities give commuters a way to increase occupancy. For locales where such services are lacking, online rideshare communities can serve a similar purpose.
Houston is a city which employs reversible HOV lanes. Seattle runs some of its HOV lanes in the express lanes of I-5 and I-90; others run in the mainline, outside of the express lane area. San Diego uses a reversible, separated 2-lane HOV route along an eight mile stretch of I-15 that travels south-bound in the morning and north-bound in the afternoon and evening. This route also doubles as a toll-road for single occupant vehicles using the CalTrans FasTrak system. Montreal employs reversible lanes on Park Avenue, and has reversible bus lanes on the Champlain Bridge. The Crescent City Connection in New Orleans features two reversible HOV lanes.
Some also point out that the traffic speed differential between HOV and general purpose lanes creates a potentially dangerous situation if the HOV lanes are not separated by a barrier. (A Texas Transportation Institute study found that HOV lanes lacking barrier separations caused a 50% increase in injury crashes.)
Critics cite recent unpublished research of San Francisco-area HOV lanes that found the HOV system increased congestion, delays, and pollution while not increasing carpooling.
The National Motorists Association in the U.S. opposes HOV lanes on the grounds that motorists are entitled to full use of highway systems paid for by their taxes.
In the Netherlands, the first HOV lane in Europe was opened on the Rijksweg 1 on 27 October 1993. On the first day, a former Minister of Transport and Water Management drove on the lane alone in his car in order to draw forth a test case. The judge ruled that Dutch traffic law didn't know the concept of a "carpool" and that the principle of equality was violated. A few years later the lane was opened to all traffic.
When HOV lanes were first introduced in California in the 1970s, some drivers placed an inflatable person in the passenger seat in an attempt to fool regulators. This was soon outlawed, but the practice persists. In the UK in 2005, a camera that was claimed to distinguish mannequins or dolls from humans was being tested on the Forth Road Bridge in an effort to thwart cheaters.