Қозғалысты реттеуге арналған шамдар туралы ақпарат

Signaling device to control competing flows of traffic
lights used for signalling

Traffic lights, traffic signals, or stoplights – also known as robots in South Africa and Namibia – are signalling devices positioned at road intersections, pedestrian crossings, and other locations in order to control the flow of traffic. Traffic lights consist normally of three signals, transmitting meaningful information to road users through colours and symbols including arrows and bicycles. The regular traffic light colours are red, yellow (also known as amber), and green arranged vertically or horizontally in that order. Although this is internationally standardised, variations exist on national and local scales as to traffic light sequences and laws. The method was first introduced in December 1868 on Parliament Square in London to reduce the need for police officers to control traffic. Since then, electricity and computerised control has advanced traffic light technology and increased intersection capacity. The system is also used for other purposes, for example, to control pedestrian movements, variable lane control (such as tidal flow systems or smart motorways), and railway level crossings.

The first system of traffic signals was installed as a way to replace police officer control of vehicular traffic outside the Houses of Parliament in London on 9 December 1868. In the first two decades of the 20th century, semaphore traffic signals like the one in London were in use all over the United States with each state having its own design of the device. In many cases, it was controlled by a traffic officer who would blow a whistle before changing the commands on this signal to help alert travellers of the change. In 1912, the first electric traffic light was developed by Lester Wire, a policeman in Salt Lake City, Utah. It was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio. The first four way, three colour traffic light was created by William Potts in Detroit, Michigan in 1920. By 1922 traffic towers were beginning to be controlled by automatic timers more widely. The main advantage of the use of the timer was that it saved cities money by replacing traffic officers. The city of New York was able to reassign all but 500 of its 6,000 officers working on the traffic squad; this saved the city $12,500,000. Garrett Morgan received a patent for the design of manually operated three way traffic light with moving arms in 1923. The control of traffic lights made a big turn with the rise of computers in America in the 1950s. One of the best historical examples of computerized control of lights was in Denver in 1952. In 1967, the city of Toronto was the first to use more advanced computers that were better at vehicle detection. The computers maintained control over 159 signals in the cities through telephone lines.

A set of lights, known as a signal head, may have one, two, three, or more aspects. The most common signal type has three aspects facing the oncoming traffic: red on top, amber (yellow) below, and green below that. Additional aspects may be fitted to the signal, usually to indicate specific restrictions or filter movements.

The 1968 Vienna Convention on Road Signs and Signals Chapter III provides international standards for the setup of traffic signal operations. Not all states have ratified the convention. A three colour signal head should have three non flashing lights which are red, amber, and green, either arranged horizontally (on the side opposite to the direction of traffic) or vertically (with red on top). A two colour signal head may be used in temporary operation and consists of red and green non flashing lights. In both cases, all lights should be circular or arrow shaped.

Arrow aspects may be used to permit certain movements or convey other messages to road users. A green arrow may display to require drivers to turn in a particular direction only or to allow drivers to continue in a particular direction when the signal is red.

Without an all red phase, cross turning traffic may be caught in a yellow trap. When the signal turns amber (also known as yellow), a turning driver may assume oncoming traffic will stop and a crash may result. For this reason, the US bans sequences that may cause a yellow trap. This can also happen when emergency vehicles or railroads preempt normal signal operation. In the United States, signs reading "Oncoming traffic has extended green" or "Oncoming traffic may have extended green" must be posted at intersections where the "yellow trap" condition exists.

South Korea has implemented special LED ribbon embedded to the ground for pedestrian crossing which allows pedestrian to be fully immersed to his smartphone experience. By this additional signal the smartphone user does not need to lift his sight from the device to know when it is safe to cross.

In some jurisdictions such as Australia, pedestrian lights are associated with a sound device, for the benefit of blind and visually impaired pedestrians. These make a slow beeping sound when the pedestrian lights are red and a continuous buzzing or fast beeping sound when the lights are green. In the Australian States of Queensland, New South Wales, Victoria, and Western Australia, the sound is produced in the same unit as the push buttons. In a circle above the button, the sound is produced and can be felt along with a raised arrow that points in the direction to walk. This system of assistive technology is also widely used at busy intersections in Canadian cities. In the United Kingdom, the Puffin crossings and their predecessor, the Pelican crossing, will make a fast beeping sound to indicate that it is safe to cross the road. The beeping sound is disabled during the nighttime so as not to disturb any nearby residents. In some states in the United States, at some busy intersections, buttons will make a beeping sound for blind people. When the light changes, a speaker built into the button will play a recording to notify blind people that it is safe to cross. When the signal flashes red, the recording will start to count down with the countdown timer. In several countries such as New Zealand, technology also allows deaf and blind people to feel when lights have changed to allow safe crossing. A small pad, housed within an indentation in the base of the box housing the button mechanism, moves downwards when the lights change to allow crossing. This is designed to be felt by anyone waiting to cross who has limited ability to detect sight or sound. In Japan, a traffic light emits an electronic sound that mimics the sound of birdsong to help the visually impaired. Some traffic lights fix the order and type of sound so that they can tell which direction is a green light. In general, "Piyo" (peep) and "Piyo piyo", which is a small bird call, and "Kakkō" and "Ka kakkō", which is a cuckoo call, are associated with this system. Some pedestrian crossings in Lithuania make a slow beeping sound indicating that the traffic light is about to turn off.

Where cycle lanes or cycle tracks exist on the approach to a signal controlled junction, it must be considered how to incorporate cyclists safely into the junction to reduce conflict between motor vehicles and cyclists. An advanced stop line can be placed after the stop line at traffic lights. This allows cyclists to position themselves in front of traffic at a red light and get a headstart. In the US, design advice typically advises that the cycle lane should continue through the junction to the left of the right turn lane; however, this creates conflict where motor vehicles wish to enter the right lane, as they must cross the cycle lane at a bad angle. Under Dutch engineering principles, cyclists are instead kept to the right of the junction, with protected kerbs. This improves safety by putting cyclists into the eyeline of motor vehicles at the stop line, allowing cyclists a headstart over turning traffic. This design also allows cyclists to complete far side turns without having to wait in the centre of the junction. Alternatively, cyclists can be considered pedestrians on approach to a junction, or where a cycle track crosses a road and combined pedestrian cyclist traffic lights (known as Toucan crossings in the UK) can be provided.

Traffic lights for public transport often use signals that are distinct from those for private traffic. They can be letters, arrows or bars of white or coloured light.

+MUTCD Fig. 8C 3 Three lens signal Two lens signal Single LRT route Stop   Prepare to stop (flashing) Stop Go Go name=2prep   Two LRT route diversion Stop   Prepare to stop (flashing) Stop Go name=samehouse Go name=2prepname=samehouse   Two LRT route diversion Stop   Prepare to stop (flashing) Stop Go name=samehouse Go name=2prepname=samehouse   Three LRT route diversion Stop   Prepare to stop (flashing) Stop Go name=samehouse Go name=2prepname=samehouse Notes
MUTCD specifies a standard vertically oriented signal with either two or three lenses, displaying white lines on a black background. Some systems use the letter B for buses and T for trams. The METRO light rail system in Minneapolis, Minnesota, the Valley Metro Rail in Phoenix, Arizona, and the RTA Streetcar System in New Orleans use a simplified variant of the Belgian/French system in the respective city's central business district where only the "go" and "stop" configurations are used. A third signal equal to amber is accomplished by flashing the "go" signal.

In some European countries and Russia, dedicated traffic signals for public transport (tram, as well any that is using a dedicated lane) have four white lights that form the letter T. If the three top lamps are lit, this means "stop". If the bottom lamp and some lamps on the top row are lit, this means permission to go in a direction shown. In the case of a tram signal, if there are no tram junctions or turns at an intersection, a simpler system of one amber signal in the form of the letter T is used instead; the tram must proceed only when the signal is lit. In North European countries, the tram signals feature white lights of different forms: "S" for "stop", "—" for "caution" and arrows to permit passage in a given direction. In Sweden, All signals use white lighting and special symbols ("S", "–" and an arrow) to distinguish them from regular signals. The Netherlands uses a distinctive "negenoog" (nine eyed) design shown on the top row of the diagram; bottom row signals are used in Belgium, Luxembourg, France, and Germany. The signals mean (from left to right): "go straight ahead", "go left", "go right", "go in any direction" (like the "green" of a normal traffic light), "stop, unless the emergency brake is needed" (equal to "amber"), and "stop" (equal to "red").

In Japan, tram signals are under the regular vehicle signal; however, the colour of the signal intended for trams is orange. The small light at the top tells the driver when the vehicle's transponder signal is received by the traffic light. In Hong Kong, an amber T signal is used for trams, in place of the green signal. In addition, at any tramway junction, another set of signals is available to indicate the direction of the tracks. In Australia and New Zealand, a white "B" or "T" sometimes replaces the green light indicating that buses or trams (respectively) have right of way.

Some regions have signals that are interruptible, giving priority to special traffic, usually emergency vehicles such as firefighting apparatus, ambulances, and police cars. Most of the systems operate with small transmitters that send radio waves, infrared signals, or strobe light signals that are received by a sensor on or near the traffic lights. Some systems use audio detection, where a certain type of siren must be used and detected by a receiver on the traffic light structure. Upon activation, the normal traffic light cycle is suspended and replaced by the "preemption sequence": the traffic lights to all approaches to the intersection are switched to "red" with the exception of the light for the vehicle that has triggered the preemption sequence. Sometimes, an additional signal light is placed nearby to indicate to the preempting vehicle that the preempting sequence has been activated and to warn other motorists of the approach of an emergency vehicle. The normal traffic light cycle resumes after the sensor has been passed by the vehicle that triggered the preemption. In lieu of preemptive mechanisms, in most jurisdictions, emergency vehicles are not required to respect traffic lights. However, emergency vehicles must slow down, proceed cautiously and activate their emergency lights to alert oncoming drivers to the preemption when crossing an intersection against the light. Unlike preemption, which immediately interrupts a signal's normal operation to serve the preempting vehicle and is usually reserved for emergency use, "priority" is a set of strategies intended to reduce delay for specific vehicles, especially mass transit vehicles such as buses. A variety of strategies exist to give priority to transit but they all generally work by detecting approaching transit vehicles and making small adjustments to the signal timing. These adjustments are designed to either decrease the likelihood that the transit vehicle will arrive during a red interval or decrease the length of the red interval for those vehicles that are stopped. Priority does not guarantee that transit vehicles always get a green light the instant they arrive as preemption does.

A variety of different control systems are used to operate signal cycles smoothly, ranging from simple clockwork mechanisms to sophisticated computerised control systems. Computerised systems are normally actuated, i. e. controlled by loop detectors or other sensors on junction approaches. Area wide coordination can allow green wave systems to be set up for vehicles or cycle tracks. Smart traffic light systems combine traditional actuation, a wider array of sensors and artificial intellegence to further improve performance of signal systems. A traffic signal junction or crossing is typically controlled by a controller mounted inside a cabinet nearby. "Phases" (or "signal groups" in Australia and New Zealand) are indications show simultaneously, e. g. multiple green lights which control the same traffic approach. A "movement" is any path through the junction which vehicles or pedestrians are permitted to take, which is "conflicting" if these paths cross one another. A stage (or "phase" in ANZ) is a group of non conflicting phases which move at the same time. The stages are collectively known as a "cycle". The time between two conflicting green phases is called an "intergreen period", which is set at an appropriate length for the junction to safely clear, especially for turning traffic which may be waiting in the centre of the junction. This often results in an all red stage, when all approaches are shown a red light and no vehicle can proceed. This all red is sometimes extended to allow a pedestrian scramble, where pedestrians can cross the empty junction in any direction all at once. Some signals have no "all red" phase: the light turns green for cross traffic the instant the other light turns red. Many traffic light installations are fitted with vehicle actuation, i. e. detection, to improve the flexibility of traffic systems to respond to varying traffic flows. Detectors come in the form of digital sensors fitted to the signal heads or induction loops within the road surface. Induction loops are beneficial due to their smaller chance of breakdown, but their simplicity can limit their ability to handle some situations, particularly involving lighter vehicles such as motorcycles or pedal cycles. This situation most often occurs at times of day when other traffic is sparse as well as when the small vehicle is coming from a direction that does not have a high volume of traffic.

The timing of the intergreen is usually based on the size of the intersection, which can range from two to five seconds. Modelling programs include the ability to calculate intergreen times automatically. Intergreen periods are determined by calculating the path distance for every conflict point in the junction, which is the distance travelled to the conflict point by the movement losing right of way minus the distance travelled to the same conflict point by the movement gaining right of way using the possible conflict points (including with pedestrians) and calculating both the time it would take the last vehicle to clear the furthest collision point and the first vehicle from the next stage to arrive at the conflict point. At actuated junctions, integreens can be varied to account for traffic conditions. Where pedestrian signals are used, the timing of the "inivitation to cross" – the period where a steady walk signal shows – and clearance periods – time when the walk signal flashes or no signal is shown – need to be calculated. This is normally set against a design speed, e. g. Similarly, these can be made extendable using sensors, allowing slower moving pedestrians more time to cross the street.

Variable lane control is a form of intelligent transportation systems which involve the use of lane use control signals, typically on a gantry above a carriageway. These lights are used in tidal flow systems to allow or forbid traffic to use one or more of the available lanes by the use of green lights or arrows (to permit) or by red lights or crosses (to prohibit). Variable lane control may be in use at toll plazas to indicate open or closed booths; during heavy traffic to facilitate merging traffic from a slip road. US based studies have found that the majority of drivers think that it is dangerous to run a red light at speed and the most common reason for red light running include inattentive driving, following an oversized vehicle or during inclement weather. The rules governing traffic light junctions for vehicles differ by jurisdiction. For example, it is common in North America that drivers can turn kerb to kerb (i. e. turning right at most junctions), even when a red light shows. On the other hand, this turn on red rule is uncommon in Europe, unless an arrow signal or traffic sign specifically permits it.

Conventional traffic signal lighting, still common in some areas, uses a standard light bulb. The light then bounces off a mirrored glass or polished aluminium reflector bowl, and out through a polycarbonate plastic or glass signal lens. In some signals, these lenses were cut to include a specific refracting pattern. Traditionally, incandescent and halogen bulbs were used. Because of the low efficiency of light output and a single point of failure (filament burnout), some traffic authorities are choosing to retrofit traffic signals with LED arrays that consume less power, have increased light output, and last significantly longer. Moreover, in the event of an individual LED failure, the aspect will still operate albeit with a reduced light output. The light pattern of an LED array can be comparable to the pattern of an incandescent or halogen bulb fitted with a prismatic lens. The low energy consumption of LED lights can pose a driving risk in some areas during winter. Unlike incandescent and halogen bulbs, which generally get hot enough to melt away any snow that may settle on individual lights, LED displays – using only a fraction of the energy – remain too cool for this to happen. As a response to the safety concerns, a heating element on the lens was developed.

Signals such as the 3M High Visibility Signal utilize light diffusing optics and a Fresnel lens to create the signal indication. The light from a 150 W PAR46 sealed beam lamp in these "programmable visibility" signals passes through a set of two glass lenses at the back of the signal. The first lens, a frosted glass diffusing lens, diffuses the light into a uniform ball of light around five inches in diameter. The light then passes through a nearly identical lens known as an optical limiter (3M's definition of the lens itself), also known as a "programming lens", also five inches in diameter. Using a special aluminium foil based adhesive tape, these signals are "masked" or programmed by the programming lens so that only certain lanes of traffic will view the indication. At the front of these programmable visibility signals is a 12" Fresnel lens, each lens tinted to meet United States Institute of Transportation Engineers (ITE) chromaticity and luminance standards. The Fresnel lens collimates the light output created by the lamp and creates a uniform display of light for the lane in which it is intended. In addition to being positioned and mounted for desired visibility for their respective traffic, some traffic lights are also aimed, louvered, or shaded to minimize misinterpretation from other lanes. For example, a Fresnel lens on an adjacent through lane signal may be aimed to prevent left turning traffic from anticipating its own green arrow. Intelight Inc. manufactures a programmable traffic signal that uses a software controlled LED array and electronics to steer the light beam toward the desired approach. The signal is programmed unlike the 3M and McCain models. It requires a connection to a laptop or smartphone with the manufacturer's software installed. Connections can be made directly with a direct serial interface kit, or wirelessly with a radio kit over WIFI to the signal. In addition to aiming, Fresnel lenses, and louvers, visors and back panels are also useful in areas where sunlight would diminish the contrast and visibility of a signal face. Typical applications for these signals were skewed intersections, specific multi lane control, left turn pocket signals, or other areas where complex traffic situations existed.

In the United States, traffic lights are currently designed with lights approximately in diameter. Previously the standard had been ; however, those are slowly being phased out in favour of the larger and more visible 12 inch lights. Variations used have also included a hybrid design, which had one or more 12 inch lights along with one or more lights of on the same light. In the United Kingdom, 12 inch lights were implemented only with Mellor Design Signal heads designed by David Mellor. These were designed for symbolic optics to compensate for the light loss caused by the symbol. However, following a study sponsored by the UK Highways Agency and completed by Aston University, Birmingham, UK, an enhanced optical design was introduced in the mid 1990s. Criticism of sunlight washout (cannot see the illuminated signal due to sunlight falling on it), and sun phantom (signal appearing to be illuminated even when not due to sunlight reflecting from the parabolic mirror at low sun angles), led to the design of a signal that used lenslets to focus light from a traditional incandescent bulb through apertures in a matt black front mask. This cured both problems in an easily manufactured solution. This design proved successful and was taken into production by a number of traffic signal manufacturers through the engineering designs of Dr. Mark Aston, working firstly at the SIRA Ltd in Kent, and latterly as an independent optical designer. The manufacturers took a licence for the generic design from the Highways Agency, with Dr. Aston engineering a unique solution for each manufacturer. Producing both bulb and LED versions of the signal aspects, these signals are still the most common type of traffic light on UK roads. With the invention of anti phantom, highly visible Aston lenses, lights of could be designed to give the same output as plain lenses, so a larger surface area was unnecessary. Consequently, lights of are no longer approved for use in the UK and all lights installed on new installations have to be in accordance with TSRGD (Traffic Signs Regulations and General Directions). Exemptions are made for temporary or replacement signals.

The MUTCD identifies five types of traffic light mounts. On pedestals, signal heads are mounted on a single pole (this is the normal installation method for the UK). Signals can either be placed nearside – between the stop line and the kerbline of the intersecting road – or farside – on the opposite side of the junction. In European countries, signals are often placed on the nearside. In the UK, at least two signal heads are required (known as the primary and secondary heads), one of which is normally nearside and the other of which could be nearside or farside. Traffic lights can increase the traffic capacity at intersections and reduce delay for side road traffic, but can also result in increased delay for main road traffic. Hans Monderman, the innovative Dutch traffic engineer, and pioneer of shared space schemes, was sceptical of their role, and is quoted as having said of them: "We only want traffic lights where they are useful and I haven't found anywhere where they are useful yet." A World Economic Forum study found that signalised junctions are linked to higher rates of localised air pollution. Drivers accelerate and stop frequently at lights and as such peak particle concentration can be around 29 times higher than during free flow conditions. The WEF recommends that traffic authorities synchronise traffic signals, consider alternative traffic management systems and consider placing traffic lights away from residential areas, schools, and hospitals. Since right angled and turn against traffic collisions are more likely to result in injuries, this is often an acceptable trade off. They can also adversely affect the safety of bicycle and pedestrian traffic. Between 1979 and 1988, the city of Philadelphia, Pennsylvania, removed signals at 199 intersections that were not warranted. On average, the intersections had 24% fewer crashes after the unwarranted signals were removed.

The symbolism of a traffic light (and the meanings of the three primary colours used in traffic lights) are frequently found in many other contexts. Since they are often used as single spots of colour without the context of vertical position, they are typically not comprehensible to up to one in ten males who are colour blind. Traffic lights have also been used in computer software, such as the macOS user interface, and in pieces of artwork, particularly Traffic Light Tree in London, UK.

Automobile racing circuits can also use standard traffic signals to indicate to racing car drivers the status of racing. On an oval track, four sets may be used, two facing a straight away and two facing the middle of the 180 degree turn between straight away. Green would indicate racing is underway, while amber would indicate to slow or while following a pace car; red would indicate to stop, probably for emergency reasons. Scuderia Ferrari, a Formula One racing team, formerly used a traffic light system during their pit stops to signal to their drivers when to leave the pits. The red light was on when the tires were being changed and fuel was being added, amber was on when the tires were changed, and green was on when all work was completed. The system is (usually) completely automatic. However, the system was withdrawn after the 2008 Singapore Grand Prix, due to the fact that it heavily delayed Felipe Massa during the race, when he was in the lead. Usually, the system was automatic, but heavy traffic in the pit lane forced the team to operate it manually. A mechanic accidentally pressed the green light button when the fuel hose was still attached to the car, causing Massa to drive off, towing the fuel hose along. Additionally, Massa drove into the path of Adrian Sutil, earning him a penalty. He finally stopped at the end of the pit lane, forcing Ferrari's mechanics to sprint down the whole of the pit lane to remove the hose. As a result of this, and the penalty he also incurred, Massa finished 13th. Ferrari decided to use a traditional "lollipop" for the remainder of the 2008 season. Another type of traffic light that is used in racing is the Christmas Tree, which is used in drag racing. The Christmas Tree has six lights: a blue staging light, three amber lights, a green light, and a red light. The blue staging light is divided into two parts: Pre stage and stage. Sometimes, there are two sets of bulbs on top of each other to represent them. Once a driver is staged at the starting line, then the starter will activate the light to commence racing, which can be done in two ways. If a Pro tree is used, then the three amber lights will flash at the same time. For the Sportsman tree, the amber light will flash from top to bottom. When the green light comes up, the race officially begins but if a driver crosses the line before that happens, then a red light will come up and that will be a foul.

The colours red, amber, and green are often used as a simple to understand rating system for products and processes. It may be extended by analogy to provide a greater range of intermediate colours, with red and green at the extremes.

In Unicode, the symbol for is HORIZONTAL TRAFFIC LIGHT and is VERTICAL TRAFFIC LIGHT.

City of Beacon. Canajoharie, New York: Credits. Retrieved 30 September 2008. Croton on Hudson Historical Society. Canajoharie, New York: Credits. Retrieved 30 September 2008. Villages of Canajoharie & Palatine Bridge. Canajoharie, New York: Credits. Retrieved 30 September 2008.