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.
CAUSES OF ROAD JAM:
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.
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 owing to increased idling, acceleration and braking.
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.
Spillover effect from congested main arteries to secondary roads and side streets as alternative routes are attempted ('rat running'), which may affect neighborhood amenity and real estate prices.
Higher chance of collisions due to tight spacing and constant stopping-and-going.
Road rage
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.
√Countermeasures
It has been suggested by some commentators that the level of congestion that society tolerates is a rational (though not necessarily conscious)[citation needed] 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.
--Road infrastructure
Junction improvements
Grade separation, using bridges (or, less often, tunnels) freeing movements from having to stop for other crossing movements
Ramp signalling, 'drip-feeding' merging traffic via traffic signals onto a congested motorway-type roadway
Reducing junctions
Local-express lanes, providing through lanes that bypass junction on-ramp and off-ramp zones
Limited-access road, roads that limit the type and amounts of driveways along their lengths
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. These pose a potential for collisions, if drivers do not notice the change in direction indicators. 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)
.
Bus lanes as part of a busway system
HOV lanes, for vehicles with at least three (sometimes at least two) riders, intended to encourage carpooling
Slugging, impromptu carpooling at HOV access points, on a hitchhiking or payment basis
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.
Transit-oriented development are residential and commercial areas designed to maximize access to public transport by providing a transit station or stop (train station, metro station, tram stop, or bus stop).
--Supply and demand
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.[14][15] 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:
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)
Creating new routes
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.
Park and ride facilities allowing parking at a distance and allowing continuation by public transport or ride sharing. Park-and-ride car parks are commonly found at metro stations, freeway entrances in suburban areas, and at the edge of smaller cities.
Reduction of road capacity to force traffic onto other travel modes. Methods include traffic calming and the shared space concept.
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.
Congestion pricing, where a certain area, such as the inner part of a congested city, is surrounded with a cordon into which entry with a car requires payment. The cordon may be a physical boundary (i.e., surrounded by toll stations) or it may be virtual, with enforcement being via spot checks or cameras on the entry routes. Major examples are Singapore's electronic road pricing, the London congestion charge system, Stockholm congestion tax and the use of High-occupancy toll lanes, predominately in North America.
Road space rationing, where regulatory restrictions prevent certain types of vehicles from driving under certain circumstances or in certain areas.
Number plate restrictions based on days of the week, as practiced in several large cities in the world, such as Athens, Mexico City, Manila and São Paulo. 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 Delanoë, the mayor of Paris, has proposed to impose a complete ban on motor vehicles in the city's inner districts,
Policy approaches, which usually attempt to provide either strategic alternatives or which encourage greater usage of existing alternatives through promotion, subsidies or restrictions.
Incentives to use public transport, increasing modal shares. This can be achieved through infrastructure investment, subsidies, transport integration, pricing strategies that decrease the marginal cost/fixed cost ratios, improved timetabling and greater priority for buses to reduce journey time e.g. [Bus Lanes], [BTR] .
Cycling promotion through legislation, cycle facilities, subsidies, and awareness campaigns.[28] The Netherlands has been pursuing cycle friendly policies for decades, and around a quarter of their commuting is done by bicycle.[29]
Promotion of more flexible work place practices. For example, a flexible workplaces pilot was undertaken in Brisbane, Australia during 2009 to test the applicability of a voluntary travel behaviour change program to achieve transport system outcomes, particularly as they related to managing congestion, either through mode shift or peak spreading. During the one-month Pilot, amongst almost 900 Brisbane CBD workers across 20 private and public sector organisations, shifts of more than 30% out of the morning and afternoon peak travel was recorded.[31]
Telecommuting encouraged through legislation and subsidies.
Online shopping promotion,[33][34] potentially with automated delivery booths helping to solve the last mile problem and reduce shopping trips made by car.[35]
Traffic management
Traffic management
Traffic congestion detector in Germany.
Use of so-called Intelligent transportation system, which guide traffic:
Traffic reporting, via radio, GPS and mobile apps, to advise road users
Variable message signs installed along the roadway, to advise road users
Navigation systems, possibly linked up to automatic traffic reporting
Traffic counters permanently installed, to provide real-time traffic counts
Convergence indexing road traffic monitoring, to provide information on the use of highway on-ramps
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[citation needed]
Parking guidance and information systems providing dynamic advice to motorists about free parking
Active Traffic Management[36] system opens up UK motorway hard shoulder as an extra traffic lane, it uses CCTV and VMS to control and monitor the traffic's use of the extra lane
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).[citation needed]
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.
Lane splitting/filtering, in which some jurisdictions allow motorcycles, scooters and bicycles to travel in the space between cars, buses, and trucks.
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