Traffic congestion is a condition on transport networks that occurs as use increases, is characterised by slower speeds, longer trip times, increased vehicular queueing. When traffic demand is great enough that the interaction between vehicles slows the speed of the traffic stream, this results in some congestion. While congestion is a possibility for any mode of transportation, this article will focus on automobile congestion on public roads; as demand approaches the capacity of a road, extreme traffic congestion sets in. When vehicles are stopped for periods of time, this is colloquially known as a traffic jam or traffic snarl-up. Traffic congestion can lead to drivers becoming engaging in road rage. Mathematically, congestion is looked at as the number of vehicles that pass through a point in a window of time, or a flow. Congestion flow lends itself to principles of fluid dynamics. Traffic congestion occurs when a volume of traffic or modal split generates demand for space greater than the available street capacity.
There are a number of specific circumstances which aggravate congestion. About half of U. S. traffic congestion is recurring, is attributed to sheer weight of traffic. Traffic research still cannot predict under which conditions a "traffic jam" may occur, it has been found that individual incidents may cause ripple effects which spread out and create a sustained traffic jam when, normal flow might have continued for some time longer. People work and live in different parts of the city. Places of work are located away from housing areas, resulting in the need for people to commute to work. According to a 2011 report published by the United States Census Bureau, a total of 132.3 million people in the United States commute between their work and residential areas daily. People may need to move about within the city to obtain goods and services, for instance to purchase goods or attend classes in a different part of the city. Brussels, a city with a strong service economy, has one of the worst traffic congestion in the world, wasting 74 hours in traffic in 2014.
This means that the city’s transportation facilities are not capable of handling the amount of traffic it receives, such as the lack of alternative routes on roads, a lack of public transportation where buses and trains are overcrowded and infrequent. In Mumbai, trains are filled to many times their capacity. Buses caught in traffic congestion are filled with passengers. Therefore, many people turn to driving their own cars to have a more pleasant commute. Thus, many people turn to driving their own cars; some traffic engineers have attempted to apply the rules of fluid dynamics to traffic flow, likening it to the flow of a fluid in a pipe. Congestion simulations and real-time observations have shown that in heavy but free flowing traffic, jams can arise spontaneously, triggered by minor events, such as an abrupt steering maneuver by a single motorist. Traffic scientists liken such a situation to the sudden freezing of supercooled fluid. However, unlike a fluid, traffic flow is affected by signals or other events at junctions that periodically affect the smooth flow of traffic.
Alternative mathematical theories exist, such as Boris Kerner's three-phase traffic theory. Because of the poor correlation of theoretical models to actual observed traffic flows, transportation planners and highway engineers attempt to forecast traffic flow using empirical models, their working traffic models use a combination of macro-, micro- and mesoscopic features, may add matrix entropy effects, by "platooning" groups of vehicles and by randomising the flow patterns within individual segments of the network. These models are typically calibrated by measuring actual traffic flows on the links in the network, the baseline flows are adjusted accordingly. A team of MIT mathematicians has developed a model that describes the formation of "phantom jams," in which small disturbances in heavy traffic can become amplified into a full-blown, self-sustaining traffic jam. Key to the study is the realization that the mathematics of such jams, which the researchers call "jamitons," are strikingly similar to the equations that describe detonation waves produced by explosions, says Aslan Kasimov, lecturer in MIT's Department of Mathematics.
That discovery enabled the team to solve traffic-jam equations that were first theorized in the 1950s. Congested roads can be seen as an example of the tragedy of the commons; because roads in most places are free at the point of usage, there is little financial incentive for drivers not to over-use them, up to the point where traffic collapses into a jam, when demand becomes limited by opportunity cost. Privatization of highways and road pricing have both been proposed as measures that may reduce congestion through economic incentives and disincentives. Congestion can happen due to non-recurring highway incidents, such as a crash or roadworks, which may reduce the road's capacity below normal levels. Economist Anthony Downs argues that rush hour traffic congestion is inevitable because of
Congestion pricing or congestion charges is a system of surcharging users of public goods that are subject to congestion through excess demand such as higher peak charges for use of bus services, metros, railways and road pricing to reduce traffic congestion. Advocates claim, this pricing strategy regulates demand, making it possible to manage congestion without increasing supply. According to the economic theory behind congestion pricing, the objective of this policy is the use of the price mechanism to make users conscious of the costs that they impose upon one another when consuming during the peak demand, that they should pay for the additional congestion they create, thus encouraging the redistribution of the demand in space or in time, forcing them to pay for the negative externalities they create, making users more aware of their impact on the environment; the application on urban roads is limited to a few cities, including London, Singapore and Gothenburg, as well as a few smaller towns, such as Durham, England.
Four general types of systems are in use. Implementation of congestion pricing has reduced congestion in urban areas, but has sparked criticism and public discontent. Critics maintain that congestion pricing is not equitable, places an economic burden on neighboring communities, has a negative effect on retail businesses and on economic activity in general, represents another tax levy. A survey of economic literature on the subject, finds that most economists agree that some form of road pricing to reduce congestion is economically viable, although there is disagreement on what form road pricing should take. Economists disagree over how to set tolls, how to cover common costs, what to do with any excess revenues and how "losers" from tolling free roads should be compensated, whether to privatize highways. Concerns regarding fossil fuel supply and urban transport high emissions of greenhouse gases in the context of climate change have renewed interest in congestion pricing, as it is considered one of the demand-side mechanisms that may reduce oil consumption.
Congestion pricing is a concept from market economics regarding the use of pricing mechanisms to charge the users of public goods for the negative externalities generated by the peak demand in excess of available supply. Its economic rationale is that, at a price of zero, demand exceeds supply, causing a shortage, that the shortage should be corrected by charging the equilibrium price rather than shifting it down by increasing the supply; this means increasing prices during certain periods of time or at the places where congestion occurs. According to the economic theory behind congestion pricing, the objective of this policy is the use of the price mechanism to make users more aware of the costs that they impose upon one another when consuming during the peak demand, that they should pay for the additional congestion they create, thus encouraging the redistribution of the demand in space or in time, or shifting it to the consumption of a substitute public good; this pricing mechanism has been used in several public utilities and public services for setting higher prices during congested periods, as a means to better manage the demand for the service, whether to avoid expensive new investments just to satisfy peak demand, or because it is not economically or financially feasible to provide additional capacity to the service.
Congestion pricing has been used by telephone and electric utilities, metros and autobus services, has been proposed for charging internet access. It has been extensively studied and advocated by mainstream transport economists for ports, waterways and road pricing, though actual implementation is rather limited due to the controversial issues subject to debate regarding this policy for urban roads, such as undesirable distribution effects, the disposition of the revenues raised, the social and political acceptability of the congestion charge. Congestion pricing is one of a number of alternative demand side strategies offered by economists to address traffic congestion. Congestion is considered a negative externality by economists. An externality occurs when a transaction causes costs or benefits to a third party although not from the use of a public good: for example, if manufacturing or transportation cause air pollution imposing costs on others when making use of public air. Congestion pricing is an efficiency pricing strategy that requires the users to pay more for that public good, thus increasing the welfare gain or net benefit for society.
Nobel-laureate William Vickrey is considered by some to be the father of congestion pricing, as he first proposed adding a distance- or time-based fare system for the New York City Subway in 1952. In the road transportation arena these theories were extended by Maurice Allais, Gabriel Roth, instrumental in the first designs and upon whose World Bank recommendation the first system was pu