High-occupancy toll lane
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 being 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 utilisation 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. 
The Los Angeles Metro ExpressLanes HOT system requires vehicles to be fitted with manually "switchable" transponders where the driver selects the number of occupants, based on which the appropriate fee is charged. California Highway Patrol officers have a device in their vehicle which displays the declared number of occupants, allowing them to visually check to see if there are more or fewer people in the car than indicated on the transponder. With the switchable transponders, the violation rate on the Metro ExpressLanes fell to 10 percent from the 20 to 25 percent cheating rate on other California HOT lanes that do not require transponders for carpoolers, prompting Alameda County officials in the San Francisco Bay Area to include the system on the then-planned lanes on Interstate 580.
Funding and construction
Implementation of these systems can be prohibitively expensive, due to the initial construction required—particularly with regard to providing access to and from the express toll lanes at interchanges. However, the long-term benefits—the decrease in delay to able motorists and increased funding for the transportation agency—may outweigh the costs. To offset costs of construction, many transportation agencies lease public roads to a private institution. As a result, construction may be partially or fully funded by the private institution, which receives all of the income from tolling for a specified period of time.
Because HOT lanes and ETLs are often constructed within the existing road space, they are criticized as being an environmental tax or perk for the rich ("Lexus lanes"). Supporters of HOT lanes note that by encouraging the use of transit and ride sharing they reduce demand and provide a benefit for all, also that the rich have many ways to ease their commute, such as buying a home closer to where they work.
- Dave Downey (2007-01-07). "The HOT lane hype". The North County Times. Retrieved 2008-07-15.
- Metropolitan Transportation Commission. "High-Occupancy-Vehicle (HOV) and High-Occupancy/Toll (HOT) Lanes: Frequently Asked Questions". Retrieved 2008-03-01.
- Urban Land Institute (ULI) (2013). "When the Road Price Is Right – Land Use, Tolls, and Congestion Pricing" (PDF). Urban Land Institute. Retrieved 2013-04-09. See Figure 2, pp.6
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- "Exempt Vehicles".
- FAQ - VA I-495 HOT Lanes Retrieved October 6, 2009
- Brookings Institution economic study on HOT Lanes
- MD I-95 Express Toll Lanes Retrieved October 6, 2009
- "Northern Virginia Transportation Alliance".
- "Golden Gate Bridge for variable toll".
- "FAQs: FasTrak". Metro ExpressLanes. Los Angeles County Metropolitan Transportation Authority. Retrieved March 3, 2013.
- "FAQs: Driving Metro ExpressLanes". Metro ExpressLanes. Los Angeles County Metropolitan Transportation Authority. Retrieved March 3, 2013.
- Metro ExpressLanes: Rules of the Road (YouTube). Los Angeles County Metropolitan Transportation Authority. July 24, 2012. 2 minutes in.
- Richards, Gary (2014-07-11). "Bay Area carpoolers must use FasTrak in express lanes under new law". San Jose Mercury News. Retrieved 2015-07-05.
- About I-495 HOT Lanes Retrieved August 31, 2009
- A Guide for HOT Lane Development (FHWA, 2003)
- "Are Lexus Lanes Really Lexus Lanes?". WLRN. 2014-06-23. Retrieved 2015-04-28.
- MTC Planning - HOV/HOT Lanes Retrieved October 6, 2009
- "HOT for Transit? Transit’s Experience of High-Occupancy Toll Lanes" (PDF). National Centre for Transit Research (Center for Neighborhood Technology) at the University of South Florida. 2014.
- Various HOT lane articles on website dedicated to road pricing
- "Impacts of Increasing Vehicle-Occupancy Requirements on HOV/HOT Lanes" (PDF). Caltrans Traffic Operations. 2013.
- "Review of Road Pricing to Reduce Congestion" (PDF). U.S. Government Accountability Office. 2012. - includes evaluation of 21 HOT lane projects in the U.S.
- "High Occupancy Toll lane Performance Under Alternative Pricing Policies" (PDF). Transportation Research Forum. 2012.
- "A Lukewarm Report Card for High-Occupancy Toll Lanes". City Labs. 2012-02-02.
- "An evaluation of a high occupnacy toll (HOT) lane demonstrator project in San Diego". Association for European Transport. 1998.