Congestion on a city road in
Moscow.
is a condition on networks that occurs as use increases, and is characterized by slower speeds, longer trip times, and increased
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, congestion is incurred. 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.
Causes
right|thumb|Congestion on a street in [[Taipei consisting primarily of
motorcycles.]]
Congestion caused by a road accident, Algarve, Portugal.
Congestion caused by evacuees fleeing
Hurricane Rita. Traffic in all lanes of the highway is traveling in the same direction.
Traffic congestion occurs when a volume of traffic or
modal split generates demand for space greater than the available road capacity, this is 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 works and weather events. Speed and flow can also affect network capacity though the relationship is complex.
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.
Mathematical theories
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.
[Critical Mass - Ball, Philip, ISBN 0-09-945786-5] 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.
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.
It is now claimed that equations can predict these in detail:
Phantom jams can form when there is a heavy volume of cars on the road. In that high density of traffic, small disturbances (a driver hitting the brake too hard, or getting too close to another car) can quickly become amplified into a full-blown, self-sustaining traffic jam...
A team of MIT mathematicians has developed a model that describes how and under what conditions such jams form, which could help road designers minimize the odds of their formation. The researchers reported their findings May 26 in the online edition of Physical Review E.
Key to the new 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.
Economic theories
India's
economic surge has resulted in a massive increase in the number of private vehicles on its roads overwhelming the transport infrastructure. Shown here is a traffic jam in
Delhi.
,
China's economic surgehas resulted in a massive increase in the number of private vehicles on its roads overwhelming the transport infrastructure. Shown here is a traffic jam in
Beijing.]]
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-utilize 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, in his books
Stuck in Traffic (1992) and
Still Stuck in Traffic (2004), 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.
Road pricing itself is controversial, more information is available in the dedicated article.
Classification
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.
Negative impacts
Traffic congestion detector in Germany.
Traffic congestion has a number of negative effects:
- Wasting time of motorists and passengers ("opportunity cost"). As a non-productive activity for most people, congestion reduces regional economic health.
- Delays, which may result in late arrival for employment, meetings, and education, resulting in lost business, disciplinary action or other personal losses.
- Inability to forecast travel time accurately, leading to drivers allocating more time to travel "just in case", and less time on productive activities.
- Wasted fuel increasing air pollution and carbon dioxide emissions (which may contribute to global warming) owing to increased idling, acceleration and braking. Increased fuel use may also in theory cause a rise in fuel costs.
- Wear and tear on vehicles as a result of idling in traffic and frequent acceleration and braking, leading to more frequent repairs and replacements.
- Stressed and frustrated motorists, encouraging road rage and reduced health of motorists
- Emergencies: blocked traffic may interfere with the passage of emergency vehicles traveling to their destinations where they are urgently needed.
- Pollution caused by slow moving traffic. This is exacerbated if heavy diesel vehicles are part of the traffic flow.
Countermeasures
It has been suggested by some commentators 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 link it largely to subjective lifestyle choices, differentiating between car-owning and car-free households.
Road infrastructure
- * Grade separation, using bridges (or, less often, tunnels) freeing movements from having to stop for other crossing movements
- ** Local-express lanes, providing through lanes that bypass junction on-ramp and off-ramp zones
- Reversible lanes, where certain sections of highway operate in the opposite direction on different times of the day/ days of the week, to match asymmetric demand. This may be controlled by Variable-message signs or by movable physical separation
- Separate lanes for specific user groups (usually with the goal of higher people throughput with fewer vehicles)
- * HOV lanes, for vehicles with at least three (sometimes at least two) riders, intended to encourage carpooling
- ** Market-based carpooling with pre-negotiated financial incentives for the driver
Urban planning and design
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.
- Grid plans including Fused Grid road network geometry, rather than tree-like network topology which branches into cul-de-sacs (which reduce local traffic, but increase total distances driven and discourage walking by reducing connectivity). This avoids concentration of traffic on a small number of arterial roads and allows more trips to be made without a car.
- Zoning laws that encourage mixed-use development, which reduces distances between residential, commercial, retail, and recreational destinations (and encourage cycling and walking)
- Carfree cities, car-light cities, and eco-cities designed to eliminate the need to travel by car for most inhabitants.
Supply and demand
Widening works underway on the
M25 motorway to increase the number of lanes.
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). Reducing road capacity has in turn been attacked as removing free choice as well as increasing travel costs and times.
Increased supply can include:
- Adding more capacity at bottlenecks (such as by adding more lanes at the expense of hard shoulders or safety zones, or by removing local obstacles like bridge supports and widening tunnels)
- Adding more capacity over the whole of a route (generally by adding more lanes)
- Traffic management improvements (see separate section below)
Reduction of demand can include:
- Parking restrictions, making motor vehicle use less attractive by increasing the monetary and non-monetary costs of parking, introducing greater competition for limited city or road space. Most transport planning experts agree that free parking distorts the market in favour of car travel, exacerbating congestion.
- Road pricing, charging money for access onto a road/specific area at certain times, congestion levels or for certain road users
- * "Cap and trade", in which only licensed cars are allowed on the roads. A limited quota of car licences are issued each year and traded in a free market fashion. This guarantees that the number of cars does not exceed road capacity while avoiding the negative effects of shortages normally associated with quotas. However since demand for cars tends to be inelastic, the result are exorbitant purchase prices for the licenses, pricing out the lower levels of society, as seen Singapore's Certificate of Entitlement scheme.
[ - Toh, Rex S., Business Horizons, March-April, 1994]
- Road space rationing, where regulatory restrictions prevent certain types of vehicles from driving under certain circumstances or in certain areas.
In effect, such cities are banning a different part of the automobile fleet from roads each day of the week. Mainly introduced to combat
smog, these measures also reduce congestion. A weakness of this method is that richer drivers can purchase a second or third car to circumvent the ban.
- * Permits, where only certain types of vehicles (such as residents) are permitted to enter a certain area, and other types (such as through-traffic) are banned.
[ For example, Bertrand Delanoe, the mayor of Paris, has proposed to impose a complete ban on motor vehicles in the city's inner districts, with exemptions only for residents, businesses, and the disabled.]
- Policy approaches, which usually attempt to provide either strategic alternatives or which encourage greater usage of existing alternatives through promotion, subsidies or restrictions.
, improved
timetabling and greater priority for buses to reduce journey time e.g. [Bus Lanes], [BTR] .
potentially with
automated delivery booths helping to solve the
last mile problem and reduce shopping trips made by car.
Traffic management
Use of so-called
Intelligent transportation system, which guide traffic:
- Traffic counters permanently installed, to provide real-time traffic counts
- Automated highway systems, a future idea which could reduce the safe interval between cars (required for braking in emergencies) and increase highway capacity by as much as 100% while increasing travel speeds
Other associated
- School opening times arranged to avoid rush hour traffic (in some countries, private car school pickup and drop-off traffic are substantial percentages of peak hour traffic).
- Considerate driving behaviour promotion and enforcement. Driving practices such as tailgating and frequent lane changes can reduce a road's capacity and exacerbate jams. In some countries signs are placed on highways to raise awareness, while others have introduced legislation against inconsiderate driving.
- Visual barriers to prevent drivers from slowing down out of curiosity (often called "rubbernecking" in the United States). This often includes accidents, with traffic slowing down even on roadsides physically separated from the crash location. This also tends to occur at construction sites, which is why some countries have introduced rules that motorway construction has to occur behind visual barrier
- Speed limit reductions, as practiced on the M25 motorway in London. With lower speeds allowing cars to drive closer together, this increases the capacity of a road. Note that this measure is only effective if the interval between cars is reduced, not the distance itself. Low intervals are generally only safe at low speeds.
By country
Australia
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.
Measures put in place by the federal and state government to combat traffic congestion include construction of new road infrastructure and increased investment in public transport.
In Brisbane, ongoing road works projects on many major roads have caused ongoing congestion throughout the city and increased commutes considerably.
Brazil
In
Brazil the recent records of traffic jams over the major big cities are recognized by public authorities as one of the main challenges for
São Paulo,
Rio de Janeiro,
Belo Horizonte,
Brasilia,
Curitiba and
Porto Alegre, where due to the country's economic bonanza, the automobile fleets have almost doubled in several of these cities from 2000 to 2008.
According to
Time Magazine,
São Paulo has the world's worst traffic jams.
On
June 10 2009, the historical record was set with more than 182 miles (293 km) of accumulated queues out of 522 mi (835 km) 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 city still experiences severe congestion. According to experts, this is due to the accelerated rate of motorization occurring since 2003, in São Paulo the fleet is growing at a rate of 7.5% per year, with almost 1,000 new cars bought in the city every day, and the limited capacity of
public transport. The subway has only of lines, though 22 further miles 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.
Hong Kong
Hong Kong aborted a road pricing system in the 1980s due to public pressure and has since relied on a vehicle high purchase tax to discourage overall car purchasing but has developed no localised congestion management techniques.
The Netherlands
The road network in the Netherlands is one of the busiest in the world. Especially in the morning and afternoon it's very busy. Commuter traffic to and from major cities such as Amsterdam, Rotterdam, The Hague, Utrecht, Haarlem, Eindhoven, Zwolle and Amsterdam Airport Schiphol. Congestion is difficult to resolve because the Netherlands is one of the most densely populated countries of the world. There is little scope for road widening. And because every year is busier, it is more difficult to troubleshoot the problem. Payment per mile seems to be a solution, but not everyone in the Netherlands is welcoming that.
New Zealand
New Zealand has followed strongly car-oriented transport policies since after World War II (especially in the
Auckland area, where about one third of the country's population lives),
[ - Mees, Paul; Dodson, Jago; Urban Research Program Issues Paper 5, Griffith University, April 2006] and currently has one of the highest car-ownership rates per capita in the world, after the United States. Because of the negative results, congestion in the big centres is a major problem. Current measures include both the construction of new road infrastructure as well as increased investment in public transport, which had strongly declined in all cities of the country except
Wellington.
United Kingdom
In the
United Kingdom the inevitability of congestion in some urban road networks has been officially recognised 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.
United States
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.
In 2005, the three areas in the
United States with the highest levels of traffic congestion were
Los Angeles,
New York City, and
Chicago. The congestion cost for the Los Angeles area alone was estimated at US$9.325 billion.
Between 1980 and 1999 the total number of miles of vehicle travel increased by 76 percent.
National and local highway construction programs have accommodated some, but not all, of this traffic growth.
Colombia
Traffic in
Bogota always had been a problem. The excessive traffic jams cause high levels of stress in people, and are the main cause of excessive environmental pollution, since the emission of gases into the atmosphere fires and damage to the cars as they are exposed to extreme situations. The problem has been mitigated partially since the implementation in 2000 of the
TransMilenio, a
bus rapid transit system that has been improving mobility throughout the city.
Venezuela
While most of the world is troubled with high gas prices,
Venezuela has the lowest gas price in the world. They pay 0.097 strong bolivars, an equivalent of $0.03 per liter or $0.12 per gallon. Venezuela has fixed their price of gasoline at this rate since 1998, even though it is estimated that the government could save $3 billion dollars a year by cutting 30 minutes from the average drive time.
[ The Economist 11 Sep 2008 6 Nov 2008 . ]Zarhay Infante leaves home shortly after 5am on a 30km (19 miles) drive to her job in the capital. If her journey goes well, she gets there three-and-a-half hours later. Three years ago she could gotten to Caracas in 45 minutes on the motorway. According to Zarhay, “It gets worse every day.”
No president has been able to increase the price of gasoline, due to protests that arise every time there are talks of doing so.
See also
