Congestion pricing encompasses several different strategies for applying a price to heavily traveled road networks. The basic concept is to raise the price of travel as the number of travelers increases, especially when the level of traffic begins to decrease the time and reliability of travel. In the United States, "high occupancy toll" (HOT) lanes has recently become one of the most common forms of congestion pricing<ref>Federal Highway Administration. "Congestion Pricing: A Primer". October 2008. http://ops.fhwa.dot.gov/publications/fhwahop08039/cp_prim1_00.htm</ref>. HOT lanes are typically converted from existing high-occupancy vehicle (HOV) lanes, retaining the basic concept of free travel by carpools and buses, while adding the option for solo drivers to "buy in" to the lane. This strategy allows motorists who value a faster and more reliable trip on the highway to pay for such an alternative. HOT lanes do not replace the "general purpose" lanes, meaning people can continue to drive for free on the same roadway. True congestion pricing on HOT lanes requires that the price paid by solo drivers increase as the volume of cars increases. In some examples, the policy guiding price response is based on maintaining a minimum average speed in the HOT lanes, such as 55mph. If so many vehicles are buying into the HOT lanes that traffic begins to back up, the price may climb significantly, or in some cases, the HOT lanes may revert temporarily back to HOV-only. There are several ways this can be accomplished, which are explored in the examples below.
=== Directing revenue to transit ===
=== Equity questions ===
== Examples of Congestion Pricing ==