Many cities across the U.S. are currently utilizing High Occupancy Vehicle (HOV) lanes in their highway infrastructures, with the aim of decreasing congestion and improving air quality by encouraging increased use of public transportation and carpooling. High Occupancy Vehicle lanes are typically restricted to vehicles carrying two or more passengers including the driver, and motorists caught not complying with the lane's intent are subject to penalties. Such restricted expanses of road are based partly on the principle that increasing the average number of passengers per vehicle will subsequently increase the number of passengers who can utilize a particular lane of the highway at once, which will hopefully reduce the number of vehicles crowding the roadways at a given time.

The traffic flow of High Occupancy Vehicle lanes can operate in one of a few ways, depending on what system is determined to be most efficient. Concurrent flow HOV lanes are separated from the standard lanes, usually by a barrier, but accommodate traffic flowing in the same direction as the regular lanes. Another type of HOV lane, the reversible lane, is usually situated in between the opposing lanes of traffic, and its traffic flow can be redirected during different times of the day to accommodate the travel direction with the heaviest flow. For instance, a reversible HOV lane may accommodate commuters traveling into a city in the morning, but flow may change to the direction leading out of the city in the afternoon rush hour when a majority of commuters are headed the opposite direction. A third type of HOV lane, called a contra flow lane, temporarily utilizes a lane from the opposite side of the highway to accommodate heavy traffic at certain times when traffic volume is high.

When used in the proper circumstances, HOV lanes can shorten commute times for multiple passenger vehicles and lessen congestion in other lanes, though there is some question about whether the benefit is perceived as substantial enough to encourage individual drivers to carpool or utilize public transportation. Studies on the effectiveness of HOV lanes have produced mixed results. HOV lanes can certainly be beneficial in areas where the traffic flow is considerable enough for a High Occupancy Vehicle lane to actually improve traffic flow. In some cases, where use of an HOV lane did not justify restriction, HOV lanes have proven ineffective and lanes have been converted back to standard lanes.