High-occupancy vehicle lane

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. They are also known as carpool lanes or diamond lanes.

Qualified vehicles

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, on which single occupant vehicles and trucks are prohibited, called carpool lanes or diamond lanes. In some cases, single occupant vehicles are allowed provided that they are hybrid vehicles or use native fuels; motorcycles are allowed to use the lanes, as well, per Federal law allowing motorcycles to use any HOV lane on highways that receive any Federal funding. In some areas, such as Southern California and Hartford, Connecticut, 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.

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 in Highway 404 in York Region & Toronto, Ontario, Canada for instance had its shoulders widened in 2003 so they serve a dual purpose as bus lanes and accident lanes. Although full HOV lanes are available for carpooling traffic in some directions, buses still continue to use shoulders along the 404 northbound until HOV lanes are added in this direction. In Columbus, Ohio, shoulders on I-70 are HOV lanes are 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.

Theory and practice

The relative rarity of high-occupancy vehicles compared to single occupancy vehicles - estimated at 7% of the traffic - in the United States and Canada makes HOV lanes work for the drivers who can use them. 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, an HOV lane moves more people per lane at a higher speed while moving fewer vehicles.

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 like can serve a similar purpose.

Reversible lanes

Some cities that use separated HOV lanes make them reversible; i.e. usable only by inbound traffic during the morning rush and usable only by outbound traffic during the evening rush. This method met with criticism after an August 1995 incident in Pittsburgh, Pennsylvania, in which a negligent highway employee failed to close the gate preventing access to the HOV lanes of Interstate 279. This led to a high-speed head-on collision that killed six people. [1]

Separate systems

Some HOV lanes are built on totally separate roadways from their corresponding general use lanes; some are constructed on parallel roads separated by a concrete barrier, while others are built on grade-separated (i.e. elevated or underground) roadways. One example is the Harbor Freeway in Los Angeles, California, where four HOV lanes travel on the upper deck of the freeway. This type of construction is said to maintain optimal efficiency by keeping general use traffic from merging back and forth into the HOV lanes, and by maximizing space on the main roadway for general use traffic.^{[citation needed]} Additionally, major interchanges on such routes are often equipped with HOV-only ramps, which minimizes haphazard cross-freeway merging.

HOV-only highway

An extreme example is Interstate 66 in the Northern Virginia suburbs of Washington, D.C. During rush hour, on a short segment of I-66 between the Capital Beltway and the Theodore Roosevelt Bridge, the entire roadway in the direction of rush-hour traffic (eastbound in the morning, westbound in the evening) is reserved for HOV[2].

Criticism

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 tend to create more congestion at exits and interchanges where no HOV-only exits have been 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. Some transportation departments, including Caltrans, have started building special direct ramps so HOV lane users can change freeways or directly enter and exit the HOV lane without having to merge across all lanes, but these ramps and flyovers are built at great expense.

Opponents 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 50% increase in injury crashes [3].)

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.

Possible future directions

A number of cities are considering converting under-utilized HOV lanes to high-occupancy toll (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.

User phenomena

One symptom of HOV lanes that challenges the contention that HOV lanes are not effective has been the slugging phenomenon of the Washington DC metro area. "Slugging" is the term used to describe a unique form of commuting where drivers go to pre-arranged "slug lines" and pick up commuters who need a ride. The driver shouts out his destination, and people in the line going to that destination enter the car in a first come first served basis. There is very specific etiquette to the system to ensure a fair, consistent, and agreeable commute for all. Slugging benefits drivers by enabling them to use the HOV lane, benefits "sluggers" by getting them rides, and benefits the community by decreasing the number of cars on the road. It however also carries most of the risks and problems of hitch-hiking.[4]

When HOV lanes were first introduced in California in the 1970s, some drivers would place an inflatable person in the passenger seat in an attempt to fool regulators. This was soon outlawed, but the practice persists. In the UK, for example, 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 [5].

See also

• Bus lane
• Bus rapid transit
• High-occupancy toll (HOT)
• Public transit
• Toll road
• Transit lanes, the Australian equivalent to high-occupancy vehicle lanes.

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