High-occupancy toll lanes

A high-occupancy toll lane (or HOT lane) is a type of traffic lane or roadway that is available to high-occupancy vehicles and other exempt vehicles without charge; other vehicles are required to pay a variable fee that is adjusted in response to demand. Unlike toll roads, drivers have an option to use general purpose lanes, on which a fee is not charged. Express toll lanes, which are less common, operate along similar lines, but do not exempt high-occupancy vehicles.

The concept developed from high-occupancy vehicle lane (HOV) systems in order to increase use of the available capacity. Most implementations are currently in the USA.

The first practical implementation was California's formerly private toll 91 Express Lanes, in Orange County, California, in 1995, followed in 1996 by Interstate 15 north of San Diego. According to the Texas A&M Transportation Institute, by 2012 there were 294 corridor-miles of HOT/Express lanes in operation in the United States and 163 corridor-miles under construction.

Some systems are reversible, operating in one direction during the morning commute and in the reverse direction during the evening commute. It is typically collected using and electronic toll collection systems, automatic number plate recognition or at manned toll booths. Exempt vehicles typically include those with at least two, three or four occupants, those that use approved alternative fuels, motorcycles, transit vehicles and emergency vehicles.

The fee, which is displayed prominently at entry points to the lanes, is adjusted in response to demand to regulate the traffic volume and thereby provided a guaranteed minimum traffic speed and level of service.

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