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Traffic comprises
pedestrian A pedestrian is a person traveling on foot, whether walking or running. In modern times, the term usually refers to someone walking on a road or pavement, but this was not the case historically. The meaning of pedestrian is displayed with ...
s,
vehicles A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wate ...
, ridden or herded animals, trains, and other
conveyance Conveyance may refer to: * Conveyance, the documentation of the transfer of ownership of land from one party to another—see conveyancing * Public conveyance, a shared passenger transportation service * A means of transport * Water conveyance, a ...
s that use public ways (roads) for travel and transportation. Traffic laws govern and regulate traffic, while rules of the road include traffic laws and informal rules that may have developed over time to facilitate the orderly and timely flow of traffic. Organized traffic generally has well-established priorities, lanes,
right-of-way Right of way is the legal right, established by grant from a landowner or long usage (i.e. by prescription), to pass along a specific route through property belonging to another. A similar ''right of access'' also exists on land held by a gov ...
, and traffic control at
intersection In mathematics, the intersection of two or more objects is another object consisting of everything that is contained in all of the objects simultaneously. For example, in Euclidean geometry, when two lines in a plane are not parallel, their i ...
s. Traffic is formally organized in many jurisdictions, with marked
lane In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each ...
s,
junction Junction may refer to: Arts and entertainment * ''Junction'' (film), a 2012 American film * Jjunction, a 2002 Indian film * Junction (album), a 1976 album by Andrew Cyrille * Junction (EP), by Basement Jaxx, 2002 * Junction (manga), or ''Hot ...
s, intersections, interchanges,
traffic signal Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic light ...
s, or
sign A sign is an object, quality, event, or entity whose presence or occurrence indicates the probable presence or occurrence of something else. A natural sign bears a causal relation to its object—for instance, thunder is a sign of storm, or me ...
s. Traffic is often classified by type: heavy
motor vehicle A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on Track (rail transport), rails (such as trains or trams) and is used for the transportation of pe ...
(e.g.,
car A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as ...
,
truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...
), other vehicle (e.g.,
moped A moped ( ) is a type of small motorcycle, generally having a less stringent licensing requirement than full motorcycles or automobiles. The term used to mean a similar vehicle except with both bicycle pedals and a motorcycle engine. Mopeds typic ...
,
bicycle A bicycle, also called a pedal cycle, bike or cycle, is a human-powered or motor-powered assisted, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A is called a cyclist, or bicyclist. Bic ...
), and
pedestrian A pedestrian is a person traveling on foot, whether walking or running. In modern times, the term usually refers to someone walking on a road or pavement, but this was not the case historically. The meaning of pedestrian is displayed with ...
. Different classes may share
speed limit Speed limits on road traffic, as used in most countries, set the legal maximum speed at which vehicles may travel on a given stretch of road. Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed - expres ...
s and easement, or may be segregated. Some jurisdictions may have very detailed and complex rules of the road while others rely more on drivers' common sense and willingness to cooperate. Organization typically produces a better combination of
travel safety Travel is the movement of people between distant geographical locations. Travel can be done by foot, bicycle, automobile, train, boat, bus, airplane, ship or other means, with or without luggage, and can be one way or round trip. Travel c ...
and efficiency. Events which disrupt the flow and may cause traffic to degenerate into a disorganized mess include
road construction A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation. There are many types of ...
,
collisions In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great f ...
, and
debris in the roadway Road debris, a form of road hazard, is debris on or off a road. Road debris includes substances, materials, and objects that are foreign to the normal roadway environment. Debris may be produced by vehicular or non-vehicular sources, but in all ...
. On particularly busy freeways, a minor disruption may persist in a phenomenon known as
traffic wave Traffic waves, also called stop waves, ghost jams, traffic snakes or traffic shocks, are traveling disturbances in the distribution of cars on a highway. Traffic waves travel backwards relative to the cars themselves. Relative to a fixed spot on t ...
s. A complete breakdown of organization may result in
traffic congestion Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s. When traffic de ...
and
gridlock Gridlock is a form of traffic congestion where "continuous queues of vehicles block an entire network of intersecting streets, bringing traffic in all directions to a complete standstill". The term originates from a situation possible in a grid ...
. Simulations of organized traffic frequently involve
queuing theory Queueing theory is the mathematical study of waiting lines, or queues. A queueing model is constructed so that queue lengths and waiting time can be predicted. Queueing theory is generally considered a branch of operations research because the ...
,
stochastic process In probability theory and related fields, a stochastic () or random process is a mathematical object usually defined as a family of random variables. Stochastic processes are widely used as mathematical models of systems and phenomena that appea ...
es and equations of
mathematical physics Mathematical physics refers to the development of mathematics, mathematical methods for application to problems in physics. The ''Journal of Mathematical Physics'' defines the field as "the application of mathematics to problems in physics and t ...
applied to
traffic flow In mathematics and transportation engineering, traffic flow is the study of interactions between travellers (including pedestrians, cyclists, drivers, and their vehicles) and infrastructure (including highways, signage, and traffic control devi ...
.


Etymology and types

The word ''traffic'' originally meant "trade" (as it still does) and comes from the Old Italian verb ''trafficare'' and noun ''traffico''. The origin of the Italian words is unclear. Suggestions include
Catalan Catalan may refer to: Catalonia From, or related to Catalonia: * Catalan language, a Romance language * Catalans, an ethnic group formed by the people from, or with origins in, Northern or southern Catalonia Places * 13178 Catalan, asteroid #1 ...
''trafegar'' "decant", an assumed
Vulgar Latin Vulgar Latin, also known as Popular or Colloquial Latin, is the range of non-formal Register (sociolinguistics), registers of Latin spoken from the Crisis of the Roman Republic, Late Roman Republic onward. Through time, Vulgar Latin would evolve ...
verb ''transfricare'' 'rub across', an assumed Vulgar Latin combination of ''trans-'' and ''facere'' 'make or do',
Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...
''tafriq'' 'distribution', and Arabic ''taraffaqa'', which can mean 'seek profit'. Broadly, the term covers many kinds of traffic including
network traffic Network traffic or data traffic is the amount of data moving across a network at a given point of time. Network data in computer networks is mostly encapsulated in network packets, which provide the load in the network. Network traffic is the main c ...
,
air traffic Air Traffic are an English alternative rock band from Bournemouth signed to EMI Records. Formed in 2003, the band consists of Chris Wall (piano, lead vocals), David Ryan Jordan (Drums), Tom Pritchard (guitar) and Jim Maddock (bass guitar). ...
, marine traffic and rail traffic, but it is often used narrowly to mean only road traffic.


Rules of the road

Rules of the road and
driving etiquette Driving etiquette refers to the general courtesy rules communities expect drivers to follow. The term dates back to the early 1900s and the use of horse-drawn carriages. Driving etiquette typically involves being courteous and staying alert, wh ...
are the general practices and procedures that road users are required to follow. These rules usually apply to all road users, though they are of special importance to
motorists Driving is the controlled operation and movement of a vehicle, including cars, motorcycles, trucks, buses, and bicycles. Permission to drive on public highways is granted based on a set of conditions being met and drivers are required to fol ...
and
cyclists Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of Bicycle, cycles for transport, recreation, Physical exercise, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", ...
. These rules govern interactions between vehicles and with
pedestrians A pedestrian is a person traveling on foot, whether walking or running. In modern times, the term usually refers to someone walking on a road or Road surface, pavement, but this was not the case historically. The meaning of pedestrian is dis ...
. The basic traffic rules are defined by an international treaty under the authority of the United Nations, the 1968 ''
Vienna Convention on Road Traffic The Convention on Road Traffic, commonly known as the Vienna Convention on Road Traffic, is an international treaty designed to facilitate international road traffic and to increase road safety by establishing standard traffic rules among the co ...
''. Not all countries are signatory to the convention and, even among signatories, local variations in practice may be found. There are also unwritten local rules of the road, which are generally understood by local drivers. As a general rule, drivers are expected to avoid a collision with another vehicle and pedestrians, regardless of whether or not the applicable rules of the road allow them to be where they happen to be. In addition to the rules applicable by default,
traffic sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduce ...
s and
traffic light Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
s must be obeyed, and instructions may be given by a police officer, either routinely (on a busy crossing instead of traffic lights) or as
road traffic control : ''For the road traffic science, see various articles under Road traffic management.'' Road traffic control involves directing vehicular and pedestrian traffic around a construction zone, accident or other road disruption, thus ensuring the safety ...
around a construction zone, accident, or other road disruption. These rules should be distinguished from the mechanical procedures required to operate a vehicle; see ''
Driving Driving is the controlled operation and movement of a vehicle, including cars, motorcycles, trucks, buses, and bicycles. Permission to drive on public highways is granted based on a set of conditions being met and drivers are required to fol ...
''. Closely related articles: *
Rules of the Road (Ireland) The Rules of the Road is the official road user guide for Ireland. See also * The Highway Code * Driver's education External linksRules of the Roadis the official online home of the Irish Rules of the Road Ireland Ireland ( ; ga, Éir ...
*
Rules of the road in China The Road Traffic Safety Law of the People's Republic of China () is a law which was passed by the Standing Committee of the National People's Congress of the People's Republic of China on October 28, 2003, promulgated by Decree No. 8 of the Presiden ...


Directionality

Traffic heading in inverse ways ought to be isolated so as to not hinder each other's way. The most essential guideline is whether to utilize the left or right half of the street.


Traffic regulations

In many countries, the rules of the road are codified, setting out the legal requirements and
punishments Punishment, commonly, is the imposition of an undesirable or unpleasant outcome upon a group or individual, meted out by an authority—in contexts ranging from child discipline to criminal law—as a response and deterrent to a particular acti ...
for breaking them. In
the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
, the rules are set out in the
Highway Code ''The Highway Code'' is a set of information, advice, guides and mandatory rules for road users in the United Kingdom. Its objective is to promote road safety. The ''Highway Code'' applies to all road users including pedestrians, horse riders ...
, which includes not only obligations but also advice on how to drive sensibly and safely. In
the United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, traffic laws are regulated by the states and municipalities through their respective
traffic code Traffic codes are laws that generally include provisions relating to the establishment of authority and enforcement procedures, statement of the Traffic#Rules of the road, rules of the road, and other safety provisions. Administrative regulations ...
s. Most of these are based at least in part on the
Uniform Vehicle Code For driving in the United States, each state and territory has its own traffic code or rules of the road, although most of the rules of the road are similar for the purpose of uniformity, given that all states grant reciprocal driving privileges ( ...
, but there are variations from state to state. In states such as Florida,
traffic law Traffic codes are laws that generally include provisions relating to the establishment of authority and enforcement procedures, statement of the Traffic#Rules of the road, rules of the road, and other safety provisions. Administrative regulations ...
and
criminal law Criminal law is the body of law that relates to crime. It prescribes conduct perceived as threatening, harmful, or otherwise endangering to the property, health, safety, and moral welfare of people inclusive of one's self. Most criminal law i ...
are separate; therefore, unless someone flees the scene of an accident or commits vehicular homicide or manslaughter, they are only guilty of a minor traffic offense. However, states such as
South Carolina )''Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...
have completely criminalized their traffic law, so, for example, one is
guilty Guilty or The Guilty may refer to: * Guilt (emotion), an experience that occurs when a person believes they have violated a moral standard Law *Culpability, the degree to which an agent can be held responsible for action or inaction *Guilt (law) ...
of a misdemeanor simply for travelling 5 miles over the speed limit.


Organized traffic


Priority (right of way)

Vehicles often come into conflict with other vehicles and pedestrians because their intended courses of travel intersect, and thus interfere with each other's routes. The general principle that establishes who has the right to go first is called "right of way", or "priority". It establishes who has the right to use the conflicting part of the road and who has to wait until the other does so. Signs, signals, markings and other features are often used to make priority explicit. Some signs, such as the
stop sign A stop sign is a traffic sign designed to notify drivers that they must come to a complete stop and make sure the intersection is safely clear of vehicles and pedestrians before continuing past the sign. In many countries, the sign is a red oc ...
, are nearly universal. When there are no signs or markings, different rules are observed depending on the location. These default priority rules differ between countries, and may even vary within countries. Trends toward uniformity are exemplified at an international level by the
Vienna Convention on Road Signs and Signals The Convention on Road Signs and Signals, commonly known as the Vienna Convention on Road Signs and Signals, is a multilateral treaty designed to increase road safety and aid international road traffic by standardising the signing system for roa ...
, which prescribes standardized traffic control devices (signs, signals, and markings) for establishing the right of way where necessary. Crosswalks (or pedestrian crossings) are common in populated areas, and may indicate that pedestrians have priority over vehicular traffic. In most modern cities, the
traffic signal Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic light ...
is used to establish the right of way on the busy roads. Its primary purpose is to give each road a duration of time in which its traffic may use the intersection in an organized way. The intervals of time assigned for each road may be adjusted to take into account factors such as difference in volume of traffic, the needs of pedestrians, or other traffic signals. Pedestrian crossings may be located near other traffic control devices; if they are not also regulated in some way, vehicles must give priority to them when in use. Traffic on a public road usually has priority over other traffic such as traffic emerging from private access; rail crossings and
drawbridge A drawbridge or draw-bridge is a type of moveable bridge typically at the entrance to a castle or tower surrounded by a moat. In some forms of English, including American English, the word ''drawbridge'' commonly refers to all types of moveable ...
s are typical exceptions.


Uncontrolled traffic

Uncontrolled traffic comes in the absence of
lane markings In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each ...
and traffic control signals. On roads without marked lanes, drivers tend to keep to the appropriate side if the road is wide enough. Drivers frequently overtake others. Obstructions are common. Intersections have no signals or signage, and a particular road at a busy intersection may be dominant – that is, its traffic flows – until a break in traffic, at which time the dominance shifts to the other road where vehicles are queued. At the intersection of two perpendicular roads, a traffic jam may result if four vehicles face each other side-on.


Turning

Drivers often seek to turn onto another road or onto
private property Private property is a legal designation for the ownership of property by non-governmental legal entities. Private property is distinguishable from public property and personal property, which is owned by a state entity, and from collective or ...
. The vehicle's blinking
turn signal The lighting system of a motor vehicle consists of lighting and signalling devices mounted to or integrated into the front, rear, sides, and in some cases the top of a motor vehicle. They illuminate the road ahead for the driver and increase th ...
s (commonly known as "blinkers" or "indicators") are often used as a way to announce one's intention to turn, thus alerting other drivers. The actual usage of directional signals varies greatly amongst countries, although its purpose is to indicate a driver's intention to depart from the current (and natural) flow of traffic well before the departure is executed (typically 3 seconds as a guideline). This will usually mean that turning traffic must stop and wait for a breach to turn, and this might cause inconvenience for drivers that follow them but do not want to turn. This is why dedicated lanes and protected traffic signals for turning are sometimes provided. On busier intersections where a protected lane would be ineffective or cannot be built, turning may be entirely prohibited, and drivers will be required to "drive around the block" in order to accomplish the turn. Many cities employ this tactic quite often; in San Francisco, due to its common practice, making three right turns is known colloquially as a "San Francisco left turn". Likewise, as many intersections in
Taipei City Taipei (), officially Taipei City, is the Capital city, capital and a Special municipality (Taiwan), special municipality of the Taiwan, Republic of China (Taiwan). Located in Regions of Taiwan, Northern Taiwan, Taipei City is an enclave of t ...
are too busy to allow direct left turns, signs often direct drivers to drive around the block to turn. Turning rules are by no means universal. For example, in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
(a drive-on-the-left country) between 1977 and 2012, left turning traffic had to give way to opposing right-turning traffic wishing to take the same road (unless there were multiple lanes, but then one must take care in case a vehicle jumped lanes). New Zealand abolished this particular rule on 25 March 2012, except at
roundabout A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford En ...
s or when denoted by a Give Way or Stop sign. Although the rule caused initial driver confusion, and many intersections required or still require modification, the change is predicted to eventually prevent one death and 13 serious injuries annually. On roads with multiple lanes, turning traffic is generally expected to move to the lane closest to the direction they wish to turn. For example, traffic intending to turn right will usually move to the rightmost lane before the intersection. Likewise, left-turning traffic will move to the leftmost lane. Exceptions to this rule may exist where for example the traffic authority decides that the two rightmost lanes will be for turning right, in which case drivers may take whichever of them to turn. Traffic may adapt to informal patterns that rise naturally rather than by force of authority. For example, it is common for drivers to observe (and trust) the turn signals used by other drivers in order to make turns from other lanes. If several vehicles on the right lane are all turning right, a vehicle may come from the next-to-right lane and turn right as well, in parallel with the other right-turning vehicles.


Intersections

In most of
Continental Europe Continental Europe or mainland Europe is the contiguous continent of Europe, excluding its surrounding islands. It can also be referred to ambiguously as the European continent, – which can conversely mean the whole of Europe – and, by ...
, the default rule is to give
priority to the right Priority to the right is a right-of-way system, in which the driver of a vehicle is required to give way to vehicles approaching from the right at intersections. The system is stipulated in Article 18.4.a of the Vienna Convention on Road Traffic fo ...
, but this may be overridden by signs or road markings. There, priority was initially given according to the social rank of each traveler, but early in the life of the automobile this rule was deemed impractical and replaced with the ''priorité à droite'' (priority to the right) rule, which still applies. At a
traffic circle A roundabout is a type of circular intersection (road), intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The N ...
where ''priorité à droite'' is not overridden, traffic on what would otherwise be a
roundabout A roundabout is a type of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.''The New Shorter Oxford En ...
gives way to traffic entering the circle. Most French roundabouts now have give-way signs for traffic entering the circle, but there remain some notable exceptions that operate on the old rule, such as the
Place de l'Étoile Place Charles de Gaulle (), historically known as the Place de l'Étoile (), is a large road junction in Paris, France, the meeting point of twelve straight avenues (hence its historic name, which translates as "Square of the Star") including t ...
around the
Arc de Triomphe The Arc de Triomphe de l'Étoile (, , ; ) is one of the most famous monuments in Paris, France, standing at the western end of the Champs-Élysées at the centre of Place Charles de Gaulle, formerly named Place de l'Étoile—the ''étoile'' ...
. Priority to the right where used in continental Europe may be overridden by an ascending hierarchy of markings, signs, signals, and authorized persons. In the United Kingdom, priority is generally indicated by signs or markings, so that almost all junctions between public roads (except those governed by traffic signals) have a concept of a major road and minor road. The default give-way-to-the-right rule used in Continental Europe causes problems for many British and Irish drivers who are accustomed to having right of way by default unless otherwise indicated. A very small proportion of low-traffic junctions are unmarked – typically on
housing estate A housing estate (or sometimes housing complex or housing development) is a group of homes and other buildings built together as a single development. The exact form may vary from country to country. Popular throughout the United States a ...
s or in rural areas. Here the rule is to "proceed with great care" i.e. slow the vehicle and check for traffic on the intersecting road. Other countries use various methods similar to the above examples to establish the right of way at intersections. For example, in most of the United States, the default priority is to yield to traffic from the right, but this is usually overridden by traffic control devices or other rules, like the
boulevard rule The boulevard rule is a principle in United States traffic law which states that the driver of a vehicle entering a highway from a smaller road or entrance (called the ''unfavored driver'') must stop and yield the right of way to all highway traffi ...
. This rule holds that traffic entering a major road from a smaller road or alley must yield to the traffic of the busier road, but signs are often still posted. The boulevard rule can be compared with the above concept of a major and minor road, or the priority roads that may be found in countries that are parties to the Vienna Convention on Road Signs and Signals. Perpendicular intersections Also known as a "four-way" intersection, this intersection is the most common configuration for roads that cross each other, and the most basic type. If
traffic signal Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic light ...
s do not control a four-way intersection, signs or other features are typically used to control movements and make clear priorities. The most common arrangement is to indicate that one road has priority over the other, but there are complex cases where all traffic approaching an intersection must yield and may be required to stop. In the United States, South Africa, and Canada, there are four-way intersections with a
stop sign A stop sign is a traffic sign designed to notify drivers that they must come to a complete stop and make sure the intersection is safely clear of vehicles and pedestrians before continuing past the sign. In many countries, the sign is a red oc ...
at every entrance, called four-way stops. A failed signal or a flashing red light is equivalent to a four-way stop, or an
all-way stop An all-way stop – also known as a four-way stop (or three-way stop etc. as appropriate) – is a traffic management system which requires vehicles on all the approaches to a road intersection to stop at the intersection before proceeding throu ...
. Special rules for four-way stops may include: # In the countries that use four-way stops, pedestrians always have priority at crosswalks – even at unmarked ones, which exist as the logical continuations of the sidewalks at every intersection with approximately right angles – unless signed or painted otherwise. # Whichever vehicle first stops at the stop line – or before the crosswalk, if there is no stop line – has priority. # If two vehicles stop at the same time, priority is given to the vehicle on the right. # If several vehicles arrive at the same time, a right-of-way conflict may arise wherein no driver has the legal right-of-way. This may result in drivers informally signaling to other drivers to indicate their intent to yield, for example by waving or flashing headlights. In Europe and other places, there are similar intersections. These may be marked by special signs (according to the
Vienna Convention on Road Signs and Signals The Convention on Road Signs and Signals, commonly known as the Vienna Convention on Road Signs and Signals, is a multilateral treaty designed to increase road safety and aid international road traffic by standardising the signing system for roa ...
), a danger sign with a black X representing a crossroads. This sign informs drivers that the intersection is uncontrolled and that default rules apply. In Europe and in many areas of North America the default rules that apply at uncontrolled four-way intersections are almost identical: # Rules for pedestrians differ by country, in the United States and Canada pedestrians generally have priority at such an intersection. # All vehicles must give priority to any traffic approaching from their right, # Then, if the vehicle is turning right or continuing on the same road it may proceed. # Vehicles turning left must also give priority to traffic approaching from the opposite direction, unless that traffic is also turning left. # If the intersection is congested, vehicles must alternate directions and/or circulate priority to the right one vehicle at a time.


Protected intersection for bicycles

A number of features make this
protected intersection A protected intersection or protected junction, also known as a Dutch-style junction, is a type of at-grade road junction in which cyclists and pedestrians are separated from cars. The primary aim of junction protection is to make pedestrians and ...
. A corner refuge island, a setback crossing of the pedestrians and cyclists, generally between 1.5–7 metres of setback, a forward stop bar, which allows cyclists to stop for a
traffic light Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
well ahead of motor traffic who must stop behind the crosswalk. Separate signal staging or at least an advance green for cyclists and pedestrians is used to give cyclists and pedestrians no conflicts or a head start over traffic. The design makes a right turn on red, and sometimes left on red depending on the geometry of the intersection in question, possible in many cases, often without stopping. This type of intersection is common in the
bicycle-friendly Bicycle-friendly policies and practices help some people feel more comfortable about traveling by bicycle with other traffic. The level of bicycle-friendliness of an environment can be influenced by many factors including town planning and cyclin ...
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
.


Pedestrian crossings

Pedestrians must often cross from one side of a road to the other, and in doing so may come into the way of vehicles traveling on the road. In many places pedestrians are entirely left to look after themselves, that is, they must observe the road and cross when they can see that no traffic will threaten them. Busier cities usually provide
pedestrian crossings A pedestrian crossing (or crosswalk in American English) is a place designated for pedestrians to cross a road, street or avenue. The term "pedestrian crossing" is also used in the Vienna and Geneva Conventions, both of which pertain to road sig ...
, which are strips of the road where pedestrians are expected to cross. The actual appearance of pedestrian crossings varies greatly, but the two most common appearances are: (1) a series of lateral white stripes or (2) two longitudinal white lines. The former is usually preferred, as it stands out more conspicuously against the dark pavement. Some pedestrian crossings accompany a
traffic signal Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control flows of traffic. Traffic light ...
to make vehicles stop at regular intervals so pedestrians can cross. Some countries have "intelligent" pedestrian signals, where the pedestrian must push a button in order to assert his intention to cross. In some countries, approaching traffic is monitored by radar or by electromagnetic sensors buried in the road surface, and the pedestrian crossing lights are set to red if a speed infringement is detected. This has the effect of enforcing the local speed limit. See Speed Limits below. Pedestrian crossings without traffic signals are also common. In this case, the traffic laws usually states that the pedestrian has the right of way when crossing, and that vehicles must stop when a pedestrian uses the crossing. Countries and driving cultures vary greatly as to the extent to which this is respected. In the state of Nevada the car has the right of way when the crosswalk signal specifically forbids pedestrian crossing. Some jurisdictions forbid crossing or using the road anywhere other than at crossings, termed ''
jaywalking Jaywalking is the act of pedestrians walking in or crossing a roadway that has traffic, other than at a designated crossing point, or otherwise, in disregard of traffic rules. The term originated in the United States as a derivation of the phras ...
''. In other areas, pedestrians may have the right to cross where they choose, and have right of way over vehicular traffic while crossing. In most areas, an intersection is considered to have a crosswalk, even if not painted, as long as the roads meet at approximate right angles.
The United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
and
Croatia , image_flag = Flag of Croatia.svg , image_coat = Coat of arms of Croatia.svg , anthem = "Lijepa naša domovino"("Our Beautiful Homeland") , image_map = , map_caption = , capit ...
are among the exceptions. Pedestrian crossings may also be located away from intersections.


Level crossings

A level crossing is an at-grade intersection of a railway by a road. Because of safety issues, they are often equipped with closable gates, crossing bells and warning signs.


Speed limits

The higher the speed of a vehicle, the more difficult collision avoidance becomes and the greater the damage if a collision does occur. Therefore, many countries of the world limit the maximum speed allowed on their roads. Vehicles are not supposed to be driven at speeds which are higher than the posted maximum. To enforce speed limits, two approaches are generally employed. In the United States, it is common for the police to patrol the streets and use special equipment (typically a
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
unit) to measure the speed of vehicles, and pull over any vehicle found to be in violation of the speed limit. In
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, Colombia and some European countries, there are computerized speed-measuring devices spread throughout the city, which will automatically detect speeding drivers and take a photograph of the license plate (or number plate), which is later used for applying and mailing the ticket. Many jurisdictions in the U.S. use this technology as well. A mechanism that was developed in Germany is the Grüne Welle, or ''
green wave A green wave occurs when a series of traffic lights (usually three or more) are coordinated to allow continuous traffic flow over several intersections in one main direction. Any vehicle traveling along with the green wave (at an approximate spe ...
'', which is an indicator that shows the optimal speed to travel for the synchronized green lights along that corridor. Driving faster or slower than the speed set by the behavior of the lights causes the driver to encounter many red lights. This discourages drivers from speeding or impeding the flow of traffic. See related
traffic wave Traffic waves, also called stop waves, ghost jams, traffic snakes or traffic shocks, are traveling disturbances in the distribution of cars on a highway. Traffic waves travel backwards relative to the cars themselves. Relative to a fixed spot on t ...
and Pedestrian Crossings, above.


Overtaking

''Overtaking'' (or ''passing'') refers to a maneuver by which one or more vehicles traveling in the same direction are passed by another vehicle. On two-lane roads, when there is a split line or a dashed line on the side of the overtaker, drivers may overtake when it is safe. On multi-lane roads in most jurisdictions, overtaking is permitted in the "slower" lanes, though many require a special circumstance. See "Lanes" below. In the United Kingdom and Canada, notably on extra-urban roads, a solid white or yellow line closer to the driver is used to indicate that no overtaking is allowed in that lane. A double white or yellow line means that neither side may overtake. In the United States, a solid white line means that lane changes are discouraged and a double white line means that the lane change is prohibited.


Lanes

When a street is wide enough to accommodate several vehicles traveling side-by-side, it is usual for traffic to organize itself into ''lanes'', that is,
parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster of IBM ...
corridors of traffic. Some roads have one lane for each direction of travel and others have multiple lanes for each direction. Most countries apply pavement markings to clearly indicate the limits of each lane and the direction of travel that it must be used for. In other countries lanes have no markings at all and drivers follow them mostly by
intuition Intuition is the ability to acquire knowledge without recourse to conscious reasoning. Different fields use the word "intuition" in very different ways, including but not limited to: direct access to unconscious knowledge; unconscious cognition; ...
rather than visual stimulus. On roads that have multiple lanes going in the same direction, drivers may usually shift amongst lanes as they please, but they must do so in a way that does not cause inconvenience to other drivers. Driving cultures vary greatly on the issue of "lane ownership": in some countries, drivers traveling in a lane will be very protective of their right to travel in it while in others drivers will routinely expect other drivers to shift back and forth. Designation and overtaking The usual designation for lanes on
divided highway A dual carriageway ( BE) or divided highway ( AE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are ...
s is the fastest lane is the one closest to the center of the road, and the slowest to the edge of the road. Drivers are usually expected to keep in the slowest lane unless
overtaking Overtaking or passing is the act of one vehicle going past another slower moving vehicle, travelling in the same direction, on a road. The lane used for overtaking another vehicle is often a passing lane farther from the road shoulder which i ...
, though with more traffic congestion all lanes are often used. When
driving on the left Left-hand traffic (LHT) and right-hand traffic (RHT) are the practices, in bidirectional traffic, of keeping to the left side or to the right side of the road, respectively. They are fundamental to traffic flow, and are sometimes referred to ...
: * The lane designated for faster traffic is on the right. * The lane designated for slower traffic is on the left. * Most freeway exits are on the left. * Overtaking is permitted to the right, and sometimes to the left. When
driving on the right Left-hand traffic (LHT) and right-hand traffic (RHT) are the practices, in bidirectional traffic, of keeping to the left side or to the right side of the road, respectively. They are fundamental to traffic flow, and are sometimes referred to ...
: * The lane designated for faster traffic is on the left. * The lane designated for slower traffic is on the right. * Most freeway exits are on the right. * Overtaking is permitted to the left, and sometimes to the right. Countries party to the
Vienna Convention on Road Traffic The Convention on Road Traffic, commonly known as the Vienna Convention on Road Traffic, is an international treaty designed to facilitate international road traffic and to increase road safety by establishing standard traffic rules among the co ...
have uniform rules about overtaking and lane designation. The convention details (amongst other things) that "Every driver shall keep to the edge of the carriageway appropriate to the direction of traffic", and the "Drivers overtaking shall do so on the side opposite to that appropriate to the direction of traffic", notwithstanding the presence or absence of oncoming traffic. Allowed exceptions to these rules include turning or heavy traffic, traffic in lines, or situation in which signs or markings must dictate otherwise. These rules must be more strictly adhered to on roads with oncoming traffic, but still apply on multi-lane and divided highways. Many countries in Europe are party to the Vienna Conventions on traffic and roads. In Australia (which is not a contracting party), traveling in any lane other than the "slow" lane on a road with a speed limit at or above is an offence, unless signage is posted to the contrary or the driver is overtaking. Many areas in North America do not have any laws about staying to the slowest lanes unless overtaking. In those areas, unlike many parts of Europe, traffic is allowed to overtake on any side, even in a slower lane. This practice is known as "passing on the right" in the United States and "overtaking on the inside" and "undertaking" in the United Kingdom. When referring to individual lanes on dual carriageways, one does not consider traffic travelling the opposite direction. The inside lane ( in the British English sense, i.e. the lane beside the hard shoulder) refers to the lane used for normal travel, while the middle lane is used for overtaking cars on the inside lane. The outside lane (i.e. closest to oncoming traffic) is used for overtaking vehicles in the middle lane. The same principle lies with dual carriageways with more than three lanes. U.S.-state-specific practices In some US states (such as
Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...
,
Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...
and
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
), although there are laws requiring all traffic on a public way to use the right-most lane unless overtaking, this rule is often ignored and seldom enforced on multi-lane roadways. Some states, such as
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...
, use a combination of laws and signs restricting speeds or vehicles on certain lanes to emphasize overtaking only on the left lane, and to avoid a psychological condition commonly called
road rage Road rage is aggressive or angry behavior exhibited by motorists. These behaviors include rude and verbal insults, yelling, physical threats or dangerous driving methods targeted at other drivers, pedestrians or cyclists in an effort to intimid ...
. In California, cars may use any lane on multi-lane roadways. Drivers moving slower than the general flow of traffic are required to stay in the right-most lanes (by
California Vehicle Code The California Vehicle Code, informally referred to as the Veh. Code or the CVC, is the section of the California Codes which contains almost all statutes relating to the operation, ownership and registration of vehicles (including bicycles and eve ...
(CVC) 21654) to keep the way clear for faster vehicles and thus speed up traffic. However, faster drivers may legally pass in the slower lanes if conditions allow (by CVC 21754). But the CVC also requires trucks to stay in the right lane, or in the right two lanes if the roadway has four or more lanes going in their direction. The oldest freeways in California, and some freeway interchanges, often have ramps on the left, making signs like "
TRUCKS OK ON LEFT LANE A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame constructi ...
" or "TRUCKS MAY USE ALL LANES" necessary to override the default rule.
Lane splitting Lane splitting is riding a bicycle or motorcycle between lanes or rows of slow moving or stopped traffic moving in the same direction. It is sometimes called whitelining, or stripe-riding. This allows riders to save time, bypassing traffic cong ...
, or riding motorcycles in the space between cars in traffic, is permitted as long as it is done in a safe and prudent manner.


One-way roadways

In order to increase traffic capacity and safety, a route may have two or more separate roads for each direction of traffic. Alternatively, a given road might be declared ''one-way''.


High-speed roads

In large cities, moving from one part of the city to another by means of ordinary streets and avenues can be time-consuming since traffic is often slowed by at-grade junctions, tight turns, narrow marked lanes and lack of a minimum
speed limit Speed limits on road traffic, as used in most countries, set the legal maximum speed at which vehicles may travel on a given stretch of road. Speed limits are generally indicated on a traffic sign reflecting the maximum permitted speed - expres ...
. Therefore, it has become common practice for larger cities to build roads for faster
through traffic Prepositions and postpositions, together called adpositions (or broadly, in traditional grammar, simply prepositions), are a class of words used to express spatial or temporal relations (''in'', ''under'', ''towards'', ''before'') or mark various ...
. There are two different types of roads used to provide high-speed access across urban areas: *The
controlled-access highway A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms i ...
(''freeway'' or ''motorway'') is a divided multi-lane highway with fully controlled access and grade-separated intersections (no cross traffic). Some freeways are called ''
expressways Expressway may refer to: *Controlled-access highway, the highest-grade type of highway with access ramps, lane markings, etc., for high-speed traffic. *Limited-access road, a lower grade of highway or arterial road. *Expressway, the fictional slide ...
'', ''super-highways'', or ''
turnpike Turnpike often refers to: * A type of gate, another word for a turnstile * In the United States, a toll road Turnpike may also refer to: Roads United Kingdom * A turnpike road, a principal road maintained by a turnpike trust, a body with powers ...
s'', depending on local usage. Access to freeways is fully controlled; entering and leaving the freeway is permitted only at grade-separated interchanges. *The
limited-access road A limited-access road, known by various terms worldwide, including limited-access highway, dual-carriageway, expressway, limited access freeway, and partial controlled access highway, is a highway or arterial road for high-speed traffic which ...
(often called ''expressway'' in areas where the name does not refer to a freeway or motorway) is a lower-grade type of road with some or many of the characteristics of a controlled-access highway: usually a broad multi-lane avenue, frequently divided, with some
grade separation In civil engineering (more specifically highway engineering), grade separation is a method of aligning a junction of two or more surface transport axes at different heights (grades) so that they will not disrupt the traffic flow on other tran ...
at intersections.
Motor vehicle A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on Track (rail transport), rails (such as trains or trams) and is used for the transportation of pe ...
drivers wishing to travel over great distances within the city will usually take the freeways or expressways in order to minimize travel time. When a crossing road is at the same
grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...
as the freeway, a bridge (or, less often, an
underpass A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube constr ...
) will be built for the crossing road. If the freeway is elevated, the crossing road will pass underneath it. Minimum speed signs are sometimes posted (although increasingly rare) and usually indicate that any vehicle traveling slower than should indicate a slower speed of travel to other motor vehicles by engaging the vehicle's four-way flashing lights. Alternative slower-than-posted speeds may be in effect, based on the posted speed limit of the highway/freeway. Systems of freeways and expressways are also built to connect distant and regional cities, notable systems include the
Interstate highways The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly known as the Interstate Highway System, is a network of controlled-access highways that forms part of the National Highway System in the United States. Th ...
, the Autobahnen and the Expressway Network of the People's Republic of China.


One-way streets

In more sophisticated systems such as large cities, this concept is further extended: some streets are marked as being ''one-way'', and on those streets all traffic must flow in only one direction. Pedestrians on the sidewalks are generally not limited to one-way movement. Drivers wishing to reach a destination they have already passed must return via other streets. One-way streets, despite the inconveniences to some individual drivers, can greatly improve traffic flow since they usually allow traffic to move faster and tend to simplify intersections.


Congested traffic

In some places traffic volume is consistently, extremely large, either during periods of time referred to as ''rush hour'' or perpetually. Exceptionally, traffic upstream of a vehicular collision or an obstruction, such as
construction Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...
, may also be constrained, resulting in a
traffic jam Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s. When traffic de ...
. Such dynamics in relation to
traffic congestion Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s. When traffic de ...
is known as
traffic flow In mathematics and transportation engineering, traffic flow is the study of interactions between travellers (including pedestrians, cyclists, drivers, and their vehicles) and infrastructure (including highways, signage, and traffic control devi ...
.
Traffic engineers Traffic engineering is a branch of civil engineering that uses engineering techniques to achieve the safe and efficient movement of people and goods on roadways. It focuses mainly on research for safe and efficient traffic flow, such as road geo ...
sometimes gauge the quality of traffic flow in terms of
level of service Level of service may refer to: * Levels of service in asset management * Level of service (transportation) in transportation and traffic * Something agreed on in a Service-level agreement A service-level agreement (SLA) is a commitment between a ...
. In measured traffic data, common spatiotemporal empirical features of traffic congestion have been found that are qualitatively the same for different highways in different countries. Some of these common features distinguish the wide moving jam and synchronized flow phases of congested traffic in Kerner's
three-phase traffic theory Three-phase traffic theory is a theory of traffic flow developed by Boris Kerner between 1996 and 2002. It focuses mainly on the explanation of the physics of traffic breakdown and resulting congested traffic on highways. Kerner describes three pha ...
.


Rush hour

During business days in most major cities,
traffic congestion Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s. When traffic de ...
reaches great intensity at predictable times of the day due to the large number of vehicles using the road at the same time. This phenomenon is called ''
rush hour A rush hour (American English, British English) or peak hour (Australian English) is a part of the day during which traffic congestion on roads and crowding on public transport is at its highest. Normally, this happens twice every weekday: on ...
'' or ''peak hour'', although the period of high traffic intensity often exceeds one hour. Since the advent of
car radio Vehicle audio is equipment installed in a car or other vehicle to provide in-car entertainment and information for the vehicle occupants. Until the 1950s it consisted of a simple AM radio. Additions since then have included FM radio (1952), 8-t ...
s, radio programming during rush hour is likely to be called
drive time Drive time is the daypart in which radio broadcasters can reach the most people who listen to car radios while driving, usually to and from work, or on public transportation. Drive-time periods are when the number of radio listeners in this c ...
.


Congestion mitigation


Rush hour policies

Some cities adopt policies to reduce rush-hour traffic and pollution and encourage the use of
public transportation Public transport (also known as public transportation, public transit, mass transit, or simply transit) is a system of transport for passengers by group travel systems available for use by the general public unlike private transport, typical ...
. For example, in
São Paulo São Paulo (, ; Portuguese for 'Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaWC a ...
,
Manila Manila ( , ; fil, Maynila, ), officially the City of Manila ( fil, Lungsod ng Maynila, ), is the capital of the Philippines, and its second-most populous city. It is highly urbanized and, as of 2019, was the world's most densely populate ...
and in
Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...
, each vehicle has a specific day of the week in which it is forbidden from traveling the roads during rush hour. The day for each vehicle is taken from the
license plate A vehicle registration plate, also known as a number plate (British English), license plate (American English), or licence plate ( Canadian English), is a metal or plastic plate attached to a motor vehicle or trailer for official identificati ...
number, and this rule is enforced by traffic police and also by hundreds of strategically positioned traffic cameras backed by computerized image-recognition systems that issue tickets to offending drivers. In the United States and Canada, several expressways have a special lane (called an "HOV Lane" –
High Occupancy Vehicle Lane A high-occupancy vehicle lane (also known as an HOV lane, carpool lane, diamond lane, 2+ lane, and transit lane or T2 or T3 lanes) is a restricted traffic lane reserved for the exclusive use of vehicles with a driver and one or more passengers, i ...
) that can only be used by cars carrying two (some locations-three) or more people. Also, many major cities have instituted strict parking prohibitions during rush hour on major arterial streets leading to and from the central business district. During designated weekday hours, vehicles parked on these primary routes are subject to prompt ticketing and towing at owner expense. The purpose of these restrictions is to make available an additional traffic lane in order to maximize available traffic capacity. Additionally, several cities offer a public telephone service where citizens can arrange rides with others depending on where they live and work. The purpose of these policies is to reduce the number of vehicles on the roads and thus reduce rush-hour traffic intensity. Metered freeways are also a solution for controlling rush hour traffic. In Phoenix, Arizona and Seattle, Washington, among other places, metered on-ramps have been implemented. During rush hour, traffic signals are used with green lights to allow one car per blink of the light to proceed on to the freeway.


Pre-emption

In some areas,
emergency responders Emergency services and rescue services are organizations that ensure public safety and health by addressing and resolving different emergencies. Some of these agencies exist solely for addressing certain types of emergencies, while others deal wit ...
are provided with specialized equipment, such as a
Mobile Infrared Transmitter A Mobile Infrared Transmitter (MIRT) is an electronic traffic preemption device that city buses and emergency vehicles use to control the traffic control equipment for intersections they are approaching, in order to pass through the intersection ...
, which allows emergency response vehicles, particularly fire-fighting apparatus, to have high-priority travel by having the lights along their route change to green. The technology behind these methods has evolved, from panels at the fire department (which could trigger and control green lights for certain major corridors) to optical systems (which the individual fire apparatus can be equipped with to communicate directly with receivers on the signal head). In certain jurisdictions, public transport buses and government-operated
winter service vehicle A winter service vehicle (WSV), or snow removal vehicle, is a vehicle specially designed or adapted to clear thoroughfares of ice and snow. Winter service vehicles are usually based on a dump truck chassis, with adaptations allowing them to carr ...
s are permitted to use this equipment to extend the length of a green light. During emergencies where evacuation of a heavily populated area is required, local authorities may institute
contraflow lane reversal Contraflow lane reversal is the altering of the normal flow of traffic, typically on a controlled-access highway (such as a freeway or motorway), to either aid in an emergency evacuation (the most common usage of the term in the United States) or, ...
, in which all lanes of a road lead away from a danger zone regardless of their original flow. Aside from emergencies, contraflow may also be used to ease traffic congestion during rush hour or at the end of a sports event (where a large number of cars are leaving the venue at the same time). For example, the six lanes of the
Lincoln Tunnel The Lincoln Tunnel is an approximately tunnel under the Hudson River, connecting Weehawken, New Jersey, to the west with Midtown Manhattan in New York City to the east. It carries New Jersey Route 495 on the New Jersey side and unsigned New Y ...
can be changed from three inbound and three outbound to a two/four configuration depending on traffic volume. The Brazilian highways
Rodovia dos Imigrantes The Rodovia dos Imigrantes (official designation SP-160) is a highway in the state of São Paulo, Brazil. The highway connects the city of São Paulo to the Atlantic coast and with the seaside cities of São Vicente and Praia Grande. It follo ...
and
Rodovia Anchieta The Rodovia Anchieta (Anchieta Highway, official designation SP-150) is a highway connection between São Paulo and the Atlantic coast, the cities of Cubatão and Santos, in Brazil. In the plateau, the highway serves several cities of Greater S ...
connect
São Paulo São Paulo (, ; Portuguese for 'Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaWC a ...
to the
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
coast. Almost all lanes of both highways are usually reversed during weekends to allow for heavy seaside traffic. The reversibility of the highways requires many additional highway ramps and complicated
interchanges Interchange may refer to: Transport * Interchange (road), a collection of ramps, exits, and entrances between two or more highways * Interchange (freight rail), the transfer of freight cars between railroad companies * Interchange station, a rai ...
.


Intelligent transportation systems

An intelligent transportation system (ITS) is a system of hardware, software, and operators-in-the-loop that allow better monitoring and control of traffic in order to optimize traffic flow. As the number of vehicle lane miles traveled per year continues to increase dramatically, and as the number of vehicle lane miles constructed per year has not been keeping pace, this has led to ever-increasing
traffic congestion Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s. When traffic de ...
. As a cost-effective solution toward optimizing traffic, ITS presents a number of technologies to reduce congestion by monitoring traffic flows through the use of sensors and live cameras or analysing cellular phone data travelling in cars (
floating car data Floating car data (FCD) in traffic engineering and management is typically timestamped geo-localization and speed data directly collected by moving vehicles, in contrast to traditional traffic data collected at a fixed location by a stationary devi ...
) and in turn rerouting traffic as needed through the use of variable message boards (VMS), highway advisory radio, on board or off board navigation devices and other systems through
integration of traffic data with navigation systems Integration of traffic data with navigation systems enables navigation systems to use traffic and other related data to optimise routing and travel times by taking into account traffic conditions and other disruptions to traffic flows. The integrat ...
. Additionally, the roadway network has been increasingly fitted with additional communications and control infrastructure to allow traffic operations personnel to monitor weather conditions, for dispatching maintenance crews to perform snow or ice removal, as well as intelligent systems such as automated bridge de-icing systems which help to prevent accidents.


See also

*
Air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airs ...
* Rules of the road in Australia *
Bicycle safety Bicycle safety is the use of road traffic safety practices to reduce risk associated with cycling. Risk can be defined as the number of incidents occurring for a given amount of cycling. Some of this subject matter is hotly debated: for example ...
*
Braess's paradox Braess's paradox is the observation that adding one or more roads to a road network can slow down overall traffic flow through it. The paradox was discovered by the German mathematician Dietrich Braess in 1968. The paradox may have analogies in ...
*
Cross-sea traffic ways Cross-sea traffic ways are vehicle or railroad traffic ways across the sea. Such traffic ways could include bridges or tunnels. Sea bridges Existing sea bridges * Anping Bridge (China) * Donghai Bridge (China) *Haicang Bridge (China) *Hangzhou Ba ...
*
Induced demand In economics, induced demand – related to latent demand and generated demandSchneider, Benjamin (September 6, 2018"CityLab University: Induced Demand"''CityLab'' – is the phenomenon whereby an increase in supply results in a decline ...
*
Institute of Transportation Engineers The Institute of Transportation Engineers (ITE) is an international educational and scientific association of transportation professionals who are responsible for meeting mobility and safety needs. ITE facilitates the application of technology and ...
*
International Regulations for Preventing Collisions at Sea The International Regulations for Preventing Collisions at Sea 1972 (COLREGs) are published by the International Maritime Organization (IMO) and set out, among other things, the "rules of the road" or navigation rules to be followed by ships a ...
* ''
Journal of Transport and Land Use The ''Journal of Transport and Land Use'' is an open access peer-reviewed academic journal covering the interaction of transport and land use that was established in 2008. As of August 2011, it is the official journal of the World Society for Tr ...
'' *
Last clear chance The last clear chance doctrine of tort law, is applicable to negligence cases in jurisdictions that apply rules of contributory negligence in lieu of comparative negligence. Under this doctrine, a negligent plaintiff can nonetheless recover if ...
*
Line source A line source, as opposed to a point source, area source, or volume source, is a source of air, noise, water contamination or electromagnetic radiation that emanates from a linear (one-dimensional) geometry. The most prominent linear sources a ...
*
Multistorey car park A multistorey car park (British and Singapore English) or parking garage (American English), also called a multistory, parking building, parking structure, parkade (mainly Canadian), parking ramp, parking deck or indoor parking, is a build ...
* Rules of the road in New Zealand *
Road traffic control device Road traffic control devices are markers, signs and signal devices used to inform, guide and control traffic, including pedestrians, motor vehicle drivers and bicyclists. These devices are usually placed adjacent, over or along the highways, roads, ...
*
Road traffic safety Road traffic safety refers to the methods and measures used to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, motorists, vehicle passengers, horse riders, and passengers of on-road ...
*
Road transport Road transport or road transportation is a type of transport using roads. Transport on roads can be roughly grouped into the transportation of goods and transportation of people. In many countries licensing requirements and safety regulations e ...
*
Rules of the road in China The Road Traffic Safety Law of the People's Republic of China () is a law which was passed by the Standing Committee of the National People's Congress of the People's Republic of China on October 28, 2003, promulgated by Decree No. 8 of the Presiden ...
*
Three-phase traffic theory Three-phase traffic theory is a theory of traffic flow developed by Boris Kerner between 1996 and 2002. It focuses mainly on the explanation of the physics of traffic breakdown and resulting congested traffic on highways. Kerner describes three pha ...
*
Traffic light Traffic lights, traffic signals, or stoplights – known also as robots in South Africa are signalling devices positioned at intersection (road), road intersections, pedestrian crossings, and other locations in order to control flows of traf ...
*
Traffic psychology Traffic psychology is a discipline of psychology that studies the relationship between psychological processes and the behavior of road users. In general, traffic psychology aims to apply theoretical aspects of psychology in order to improve traff ...
*
Traffic law Traffic codes are laws that generally include provisions relating to the establishment of authority and enforcement procedures, statement of the Traffic#Rules of the road, rules of the road, and other safety provisions. Administrative regulations ...
*
Trafficability {{Short pages monitor