Traffic congestion is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, and increased vehicular queueing. The most common example is the physical use of roads by vehicles. When traffic demand is great enough that the interaction between vehicles slows the speed of the traffic stream, this results in some congestion. As demand approaches the capacity of a road (or of the intersections along the road), extreme traffic congestion sets in. When vehicles are fully stopped for periods of time, this is colloquially known as a traffic jam or traffic snarl-up. Traffic congestion can lead to drivers becoming frustrated and engaging in road rage.
Traffic congestion occurs when a volume of traffic or modal split generates demand for space greater than the available road capacity; this point is commonly termed saturation. There are a number of specific circumstances which cause or aggravate congestion; most of them reduce the capacity of a road at a given point or over a certain length, or increase the number of vehicles required for a given volume of people or goods. About half of U.S. traffic congestion is recurring, and is attributed to sheer weight of traffic; most of the rest is attributed to traffic incidents, road work and weather events.
Traffic research still cannot fully predict under which conditions a "traffic jam" (as opposed to heavy, but smoothly flowing traffic) may suddenly occur. It has been found that individual incidents (such as accidents or even a single car braking heavily in a previously smooth flow) may cause ripple effects (a cascading failure) which then spread out and create a sustained traffic jam when, otherwise, normal flow might have continued for some time longer.
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 ("butterfly effects"), 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 often 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 (see also spatiotemporal reconstruction of traffic congestion).
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 typically use a combination of macro-, micro- and mesoscopic features, and 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 then typically calibrated by measuring actual traffic flows on the links in the network, and 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 (a driver hitting the brake too hard, or getting too close to another car) 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 also 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 the benefits of having a relatively standard work day. In a capitalist economy, goods can be allocated either by pricing (ability to pay) or by queueing (first-come first-serve); congestion is an example of the latter. Instead of the traditional solution of making the "pipe" large enough to accommodate the total demand for peak-hour vehicle travel (a supply-side solution), either by widening roadways or increasing "flow pressure" via automated highway systems, Downs advocates greater use of road pricing to reduce congestion (a demand-side solution, effectively rationing demand), in turn plowing the revenues generated therefrom into public transportation projects.
A 2011 study in the The American Economic Review indicates that there may be a "fundamental law of road congestion." The researchers, from the University of Toronto and the London School of Economics, analyzed data from the U.S. Highway Performance and Monitoring System for 1983, 1993 and 2003, as well as information on population, employment, geography, transit, and political factors. They determined that the number of vehicle-kilometers traveled (VKT) increases in direct proportion to the available lane-kilometers of roadways. The implication is that building new roads and widening existing ones only results in additional traffic that continues to rise until peak congestion returns to the previous level.
Qualitative classification of traffic is often done in the form of a six letter A-F level of service (LOS) scale defined in the Highway Capacity Manual, a US document used (or used as a basis for national guidelines) worldwide. These levels are used by transportation engineers as a shorthand and to describe traffic levels to the lay public. While this system generally uses delay as the basis for its measurements, the particular measurements and statistical methods vary depending on the facility being described. For instance, while the percent time spent following a slower-moving vehicle figures into the LOS for a rural two-lane road, the LOS at an urban intersection incorporates such measurements as the number of drivers forced to wait through more than one signal cycle.
Traffic congestion occurs in time and space, i.e., it is a spatiotemporal process. Therefore, another classification schema of traffic congestion is associated with some common spatiotemporal features of traffic congestion found in measured traffic data. Common spatiotemporal empirical features of traffic congestion are those features, which are qualitatively the same for different highways in different countries measured during years of traffic observations. Common features of traffic congestion are independent on weather, road conditions and road infrastructure, vehicular technology, driver characteristics, day time, etc. Examples of common features of traffic congestion are the features [J] and [S] for, respectively, the wide moving jam and synchronized flow traffic phases found in Kerner’s three-phase traffic theory. The common features of traffic congestion can be reconstructed in space and time with the use of the ASDA and FOTO models.
Traffic congestion has a number of negative effects:
Road rage is aggressive or angry behavior by a driver of an automobile or other motor vehicle. Such behavior might include rude gestures, verbal insults, deliberately driving in an unsafe or threatening manner, or making threats. Road rage can lead to altercations, assaults, and collisions which result in injuries and even deaths. It can be thought of as an extreme case of aggressive driving.
The term originated in the United States in 1987-1988 (specifically, from Newscasters at KTLA, a local television station), when a rash of freeway shootings occurred on the 405, 110 and 10 freeways in Los Angeles, California. These shooting sprees even spawned a response from the AAA Motor Club to its members on how to respond to drivers with road rage or aggressive maneuvers and gestures.
It has been suggested by some commentators[who?] that the level of congestion that society tolerates is a rational (though not necessarily conscious) choice between the costs of improving the transportation system (in infrastructure or management) and the benefits of quicker travel. Others[who?] link it largely to subjective lifestyle choices, differentiating between car-owning and car-free households.
City planning and urban design practices can have a huge impact on levels of future traffic congestion, though they are of limited relevance for short-term change.
Congestion can be reduced by either increasing road capacity (supply), or by reducing traffic (demand). Capacity can be increased in a number of ways, but needs to take account of latent demand otherwise it may be used more strongly than anticipated. Critics of the approach of adding capacity have compared it to "fighting obesity by letting out your belt" (inducing demand that did not exist before). For example, when new lanes are created, households with a second car that formerly was parked most of the time may begin to use this second car for commuting. Reducing road capacity has in turn been attacked as removing free choice as well as increasing travel costs and times, placing an especially high burden on the low income residents who must commute to work.
Increased supply can include:
Reduction of demand can include:
Use of so-called Intelligent transportation system, which guide traffic:
Traffic during peak hours in major Australian cities, such as Melbourne, Sydney, Brisbane and Perth, is usually very congested and can cause considerable delay for motorists. Australians rely mainly on radio and television to obtain current traffic information. GPS, webcams, and online resources are increasingly being used to monitor and relay traffic conditions to motorists.
Traffic jams have become intolerable in Dhaka. People lose valuable working hours as well as the automobiles' costly fuel every day. Although a modern city should have 25 per cent of its total area devoted to road use, Dhaka has only 7 per cent. Some other major reasons are a total absence of a rapid transit system,total absence of integrated urban planning for over thirty years,holes/pits/ditches on the roads eaten up by stagnant water due to absence of drainage system, the tendency of the drivers stop randomly park vehicles anywhere and everywhere, dilatory driving collect abrupt passengers, disorderly driving on roads, total lack of alternative routes, narrow and one-way roads and low acknowledgement of traffic signals.
According to Time magazine, São Paulo has the world's worst daily traffic jams. According to reports from the Companhia de Engenharia de Tráfego, the city's traffic management agency, the historical congestion record was set on June 1, 2012, with 295 kilometres (183 mi) of cumulative queues around the city during the evening rush hour. However, according to the firm MapLink, which tracks congestion from about 800,000 vehicles using onboard GPS, cumulative queues reached 562 kilometres (349 mi) during the same period. The previous record was set on June 10, 2009, with 293 kilometres (182 mi) of cumulative queues out of 835 kilometres (519 mi) being monitored.
Despite implementation since 1997 of road space rationing by the last digit of the plate number during rush hours every weekday, traffic in this 20-million-strong city still experiences severe congestion. According to experts, this is due to the accelerated rate of motorization occurring since 2003 and the limited capacity of public transport. In São Paulo, traffic is growing at a rate of 7.5% per year, with almost 1,000 new cars bought in the city every day. The subway has only 61 kilometres (38 mi) of lines, though 35 further kilometers are under construction or planned by 2010. Every day, many citizens spend between three up to four hours behind the wheel. In order to mitigate the aggravating congestion problem, since June 30, 2008 the road space rationing program was expanded to include and restrict trucks and light commercial vehicles.
According to the Toronto Board of Trade, in 2010, Toronto is ranked as the most congested city of 19 surveyed cities, with an average commute time of 80 minutes.
The August 2010 China National Highway 110 traffic jam in Hebei province, China, is considered the world's worst traffic jam ever, as traffic congestion stretched more than 100 kilometres (62 mi) from August 14 to the 26, including at least 11 days of total gridlock. The event was caused by a combination of road works and thousands of coal trucks from Inner Mongolia’s coalfields that travel daily to Beijing. The New York Times has called this event the "Great Chinese Gridlock of 2010."
Towards the end of 2010, Beijing announced a series of drastic measures to tackle the city's traffic jam, including limiting the number of new plates issued to passenger cars to 20,000 a month and barring cars of non-Beijing plates from entering areas within the Fifth Ring Road during rush hours.
India has a large number of increasing vehicles as the increasing number of middle class can now afford to buy the vehicles. Although India has launched various rapid transit like Delhi Metro and the Namma Metro and The Janmarg Ahemdabad BRT service but traffic is still a problem in India. India has more plans of increasing rapid transit systems.
New Zealand has followed strongly car-oriented transport policies since after World War II (especially in Auckland, where one third of the country's population lives), and currently has one of the highest car-ownership rates per capita in the world, after the United States.
In the United Kingdom the inevitability of congestion in some urban road networks has been officially recognized since the Department for Transport set down policies based on the report Traffic in Towns in 1963:
Even when everything that it is possibly to do by way of building new roads and expanding public transport has been done, there would still be, in the absence of deliberate limitation, more cars trying to move into, or within our cities than could possibly be accommodated..
The Department for Transport sees growing congestion as one of the most serious transport problems facing the UK. On 1 December 2006, Rod Eddington published a UK government-sponsored report into the future of Britain's transport infrastructure. The Eddington Transport Study set out the case for action to improve road and rail networks, as a "crucial enabler of sustained productivity and competitiveness". Eddington has estimated that congestion may cost the economy of England £22 bn a year in lost time by 2025. He warned that roads were in serious danger of becoming so congested that the economy would suffer. At the launch of the report Eddington told journalists and transport industry representatives introducing road pricing to encourage drivers to drive less was an "economic no-brainer". There was, he said "no attractive alternative". It would allegedly cut congestion by half by 2025, and bring benefits to the British economy totalling £28 bn a year.
The Texas Transportation Institute estimated that, in 2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 5.7 billion U.S. gallons (21.6 billion liters) in wasted fuel and $67.5 billion in lost productivity, or about 0.7% of the nation's GDP. It also estimated that the annual cost of congestion for each driver was approximately $1,000 in very large cities and $200 in small cities. Traffic congestion is increasing in major cities and delays are becoming more frequent in smaller cities and rural areas.
According to traffic analysis firm INRIX in 2011, the Top 10 Worst US Traffic Cities are:
1. Honolulu: Drivers waste 58 hours in traffic;
2. Los Angeles: Drivers waste 56 hours in traffic;
3. San Francisco: Drivers waste 48 hours in traffic;
4. New York: Drivers waste 57 hours in traffic;
5. Bridgeport, CT: Drivers waste 42 hours in traffic;
6. Washington, D.C.: Drivers waste 45 hours in traffic;
7. Seattle: Drivers waste 33 hours in traffic;
8. Austin: Drivers waste 30 hours in traffic;
9. Boston: Drivers waste 35 hours in traffic;
10. Chicago: Drivers waste 36 hours in traffic;
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