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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 lights consist normally of three signals, transmitting meaningful information to drivers and riders through colours and symbols including arrows and bicycles. The regular traffic light colours are red, yellow, and green arranged vertically or horizontally in that order. Although this is internationally standardised,1968, as revised 1995 and 2006
Vienna Convention on Road Signs and Signals
United Nations Publication ECE/TRANS/196. ISBN 978-92-1-116973-7. URL Accessed: 7 January 2022.
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 London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
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 Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * Tidal (servic ...
systems or smart motorways), and railway
level crossing A level crossing is an intersection where a railway line crosses a road, path, or (in rare situations) airport runway, at the same level, as opposed to the railway line crossing over or under using an overpass or tunnel. The term a ...
s.


History

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 London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
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 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 Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
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 Lester Farnsworth Wire (September 3, 1887 – April 14, 1958) was credited with the invention of the electric traffic light in 1912, in Salt Lake City. Wire worked as a detective for the Salt Lake City police force. The original traffic light, bas ...
, a policeman in
Salt Lake City Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the capital and most populous city of Utah, United States. It is the seat of Salt Lake County, the most populous county in Utah. With a population of 200,133 in 2020, th ...
,
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
. It was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in
Cleveland Cleveland ( ), officially the City of Cleveland, is a city in the United States, U.S. U.S. state, state of Ohio and the county seat of Cuyahoga County, Ohio, Cuyahoga County. Located in the northeastern part of the state, it is situated along ...
, Ohio. The first four-way, three-colour traffic light was created by police officer William Potts in
Detroit Detroit ( , ; , ) is the largest city in the U.S. state of Michigan. It is also the largest U.S. city on the United States–Canada border, and the seat of government of Wayne County. The City of Detroit had a population of 639,111 at t ...
,
Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and t ...
in 1920. He was concerned about how police officers at four different light signals could not change their lights all at the same time. The answer was a third light that was coloured yellow, which was the same colour used on the railroad. In 1922 traffic towers were beginning to be controlled by automatic timers. 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. 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 Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
in 1952. In 1967, the city of
Toronto Toronto ( ; or ) is the capital city of the Canadian province of Ontario. With a recorded population of 2,794,356 in 2021, it is the most populous city in Canada and the fourth most populous city in North America. The city is the anch ...
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.


Vehicular signals

A set of lights, known as a signal head,Traffic Signs Manual - Chapter 6: Traffic Control
''Department for Transport, Department for Infrastructure (Northern Ireland), Transport Scotland and Welsh Government''. Accessed: 18 December 2021.
may have one, two, three, or more aspects. The most common signal type has three aspects facing the oncoming traffic: red on top, amber below, and green below that. Additional aspects may be fitted to the signal, usually to indicate specific restrictions or filter movements.


Meanings of signals

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, yellow, 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.1968, as revised 1995 and 2006
Vienna Convention on Road Signs and Signals
United Nations Publication ECE/TRANS/196. ISBN 978-92-1-116973-7. URL Accessed: 7 January 2022.
Permissible signals for regulating vehicle traffic (other than public transport vehicles) are outlined in Article 23:1968, as revised 1995 and 2006
Vienna Convention on Road Signs and Signals
United Nations Publication ECE/TRANS/196. ISBN 978-92-1-116973-7. URL Accessed: 7 January 2022.
Green arrows are added to signals to indicate that drivers can travel in a particular direction, while the main lights for that approach are red, or that drivers can only travel in one particular direction. Alternatively, when combined with another green signal, they may indicate that turning traffic has priority over oncoming traffic (known as a "filter arrow"). The United States is not party to the Convention and the Manual on Uniform Traffic Control Devices (MUTCD) outlines correct operation in that country. The MUTCD specifies the following vehicular signals:2009
Manual on Uniform Traffic Control Devices for Streets and Highways: Chapter 4
US Federal Highway Administration. URL Accessed: 7 January 2022.
In the US, a single signal head shall have three, four, or five aspects (though a single aspect green arrow may be displayed to indicate a continuous movement). The signals must be arranged red, yellow, and green vertically (top to bottom) or horizontally (left to right).2009
Manual on Uniform Traffic Control Devices for Streets and Highways: Chapter 4
US Federal Highway Administration. URL Accessed: 7 January 2022.
In the US, a single-aspect flashing yellow signal can be used to raise attention to a warning sign and a single-aspect flashing red signal can be used to raise attention to a STOP, DO NOT ENTER, or WRONG WAY sign.2009
Manual on Uniform Traffic Control Devices for Streets and Highways: Chapter 4
US Federal Highway Administration. URL Accessed: 7 January 2022.
Flashing red or amber lights, known as ''intersection control beacons'', are used to reinforce stop signs at intersections.


Traffic signal cycles

Generally, at least one direction of traffic at an intersection has a green light (green aspect) at any moment in the cycle. In some jurisdictions, for a brief time, all signals at an intersection show red at the same time, to clear any traffic in the intersection. The delay can depend on traffic, road conditions, the physical layout of the intersection, and legal requirements. Thus modern signals are built to allow the "all red" in an intersection, even if the feature is not used. Some signals have no "all red" phase: the light turns green for cross traffic the instant the other light turns red.These are typically older signals. There are many examples in Houston, Texas, of this. Suspended lights constructed so that a single source simultaneously illuminates all four directions always have this characteristic: Red (in two directions) and green (in the two cross directions) with Red-Yellow-Green sequence on two sides and Green-Yellow-Red sequence on the cross sides Another variant in some locations is the pedestrian scramble, where all the traffic lights for vehicles become red, and pedestrians are allowed to walk freely, even diagonally, across the intersection. Use of the Pedestrian signals (see below) will alter the traffic signal cycle.


Variations

In the Canadian province of
Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirte ...
and the Maritime provinces, lights are often arranged horizontally, but each aspect is a different shape: red is a square (larger than the normal circle) and usually in pairs at either end of the fixture, yellow is a diamond, and green is a circle. In many southern and southwestern U.S. states, most traffic signals are similarly horizontal in order to ease wind resistance during storms and hurricanes. Japanese traffic signals mostly follow the same rule except that the "go" signals are referred to as 青 (
blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when ...
), which they historically were in fact, but this caused complications with the international "green for go" rule, so in 1973 a decree was issued that the "go" light should be changed to the bluest possible hue of green, thus making it factually greener without having to change the name from 青(blue) to 緑(green). In the UK, normal traffic lights follow this sequence: * Red – Stop, do not proceed * Red and Yellow - Get ready to proceed, but do not proceed yet * Green – Proceed if the intersection or crossing is clear, vehicles are not allowed to block the intersection or crossing * Yellow - Stop, unless it is unsafe to do so. A speed sign is a special traffic light, variable
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 ...
, or variable-message sign giving drivers a recommended speed to approach the next traffic light in its green phase and avoid a stop due to reaching the intersection when lights are red.Not completely correct: a variable speed sign is not solely used for the purpose of slowing the speed of motorists approaching an intersection. They are also used on freeways where the maximum safe speed is dependant on the conditions of the roadway (i.e. weather, falling rocks, risk of wildlife, etc.), such as in British Columbia, Canada.


Use of traffic signals in waterways, on railroads for rail traffic

The three-aspect standard is also used at locks on the Upper Mississippi River. Red means that another vessel is passing through. Amber means that the lock chamber is being emptied or filled to match the level of the approaching vessel. After the gate opens, green means that the vessel may enter. Railroad signals, for stopping trains in their own right of way, generally use the opposite positioning of the colours; that is, for signals above the driver's eyeline, green on top and red below is the standard placement of the signal colours on railroad tracks. There are three reasons for this variation: there is no risk that railway signals will be masked by a tall vehicle between the driver and the signal; train speeds in fog are much higher than for road vehicles, so it is important that the most restrictive signal is closest to the driver's eyeline; and with railway signals often in exposed rural locations, there is a risk of any signal other than the bottom one being masked by snow building up on the hood of the signal below.


Pedestrian signals

Pedestrian signals are used to inform pedestrians when to cross a road. Most pedestrian signal heads will have two lights: a 'walk' light (normally a walking human figure, typically coloured green or white) and a 'don't walk' light (normally either a red man figure or a hand), though other variations exist.


Mid-block crossings

Where pedestrians need to cross the road between junctions, a signal-controlled crossing may be provided as an alternative to a zebra crossing or uncontrolled crossing. Traffic lights are normally used at crossings where vehicle speeds are high, where either vehicle or pedestrian flows are high or near signalised junctions. In the UK, this type of crossing is called a pelican crossing, though more modern iterations are puffin and pedex crossings. In the UK, these crossings normally need at least four traffic signals, which are of a regular type (red, amber, and green), two facing in each direction. Furthermore, pedestrians will be provided with push buttons and pedestrian signals, consisting of a red and green man. Farside signals are located across the crossing, while nearside signals are located below the traffic lights, facing in the direction of oncoming traffic. A HAWK beacon is a special type of traffic used in the US at mid-block crossings. These consist of two red signals above a single yellow signal. The beacon is unlit until a pedestrian pushes the cross button. Then a yellow light will show, followed by both red lights, at which point the 'Walk' symbol will illuminate for pedestrians. At the end of the crossing phase, the 'Don't Walk' symbol will flash, as will the yellow traffic light.


Pedestrian facilities at signalised junctions

Pedestrians are usually incorporated into urban signalised junctions in one of four ways: no facilities, parallel walk, walk with traffic, or all-red phases. No facilities may be provided if pedestrian demand is low, in areas where pedestrians are not permitted, or if there is a subway or overpass. No provision of formal facilities means pedestrians will have to self-evaluate when it is safe to cross, which can be intimidating for pedestrians. With a 'parallel walk' design, pedestrians walk alongside the traffic flow. A leading pedestrian interval may be provided, whereby pedestrians get a 'walk' signal before the traffic gets a green light, allowing pedestrians to establish themselves on the crossing before vehicles begin to turn, to encourage drivers to give way. A 'walk with traffic' facility allows pedestrians to go at the same time as other traffic movements with no conflict between movements. This can work well on one-way roads, where turning movements are banned or where the straight-ahead movement runs in a different stage from the turning movement. A splitter island could also be provided. Traffic will pass on either side of the island and pedestrians can cross the road safely between the other flows. An all-red stage, also known as a full pedestrian stage or a pedestrian scramble, holds all vehicular traffic at the junction to allow pedestrians time to safely cross. This may require a longer cycle time and increase pedestrian wait periods. This can be eased by providing two pedestrian stages. This also allows diagonal crossings to be provided, known as a pedestrian scramble or the Barnes Dance, such as the famous Shibuya crossing in Tokyo. The
Barnes Dance A pedestrian scramble, also known as scramble intersection and scramble corner (Canada), 'X' Crossing (UK), diagonal crossing (US), (Japan), exclusive pedestrian interval, or Barnes Dance, is a type of traffic signal movement that temporarily s ...
is named after an American traffic engineer, Henry A. Barnes. Barnes did not claim to have invented the system but was a strong advocate of it, having observed the difficulties his daughter faced crossing the road to get to school.


Pedestrian countdown timers

Pedestrian countdown timers are becoming common at urban signal-controlled crossings. Where a pedestrian countdown is shown, it is normally used in conjunction with the flashing hand signal (in the US and Canada) or blackout period (UK), showing the amount of time remaining in seconds until the end of the flashing hand or blackout. Pedestrian countdown timers do not significantly increase or reduce the number of red- and amber-light runners (drivers). Studies have found that pedestrian countdown timers do significantly improve pedestrian compliance over traditional pedestrian signals; however, results are mixed.


Variations on pedestrian sequences


Auditory and tactile signals for impaired people

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 ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...
,
New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...
, Victoria, and
Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...
, 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 Assistive technology (AT) is a term for assistive, adaptive, and rehabilitative devices for Disability, people with disabilities and the elderly. Disabled people often have difficulty performing activities of daily living (ADLs) independently, ...
is also widely used at busy intersections in Canadian cities. In the United Kingdom, the
Puffin crossing A puffin crossing (its name derived from the phrase "pedestrian user-friendly intelligent") is a type of pedestrian crossing in use in the United Kingdom. The design is distinct from the older pelican crossing in that the lights signalling to ...
s 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 slowish beeping sound indicating that the traffic light is about to turn off.


Cycle signals

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 An advanced stop line (ASL), also called advanced stop box or bike box, is a type of road marking at signalised road junctions allowing certain types of vehicle a head start when the traffic signal changes from red to green. Advanced stop lines ...
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. UK engineers have further innovated the design by introducing the Cycle Optimised Protected Signals (CYCLOPS junction) in
Manchester Manchester () is a city in Greater Manchester, England. It had a population of 552,000 in 2021. It is bordered by the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of Salford to the west. The ...
and other cities. This places the cycle track around the edge of the signal junction and gives cyclists and pedestrians a single all-red phase, entirely separate from motor traffic and shortens pedestrian crossing times. 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. File:Cycling signals in Leipzig (3667368981).jpg,
Leipzig Leipzig ( , ; Upper Saxon: ) is the most populous city in the German state of Saxony. Leipzig's population of 605,407 inhabitants (1.1 million in the larger urban zone) as of 2021 places the city as Germany's eighth most populous, as ...
, Germany File:Traffic signals countdown.png, Countdown in the Netherlands File:Luxembourg Traffic signal pedestrian-cyclist green.JPG, Toucan symbols in Luxembourg File:Traffic signals in Austria IMG 0163.JPG, Toucan symbols with Austrian-style bike symbols File:TUCANCrossing.jpg, British toucan crossing File:Traffic Light German Complex With Bicycles.JPG, Complex German installation with transport and cycle symbols


Public transport signals

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.


By region


North America

Some systems use the letter B for buses and T for trams. The METRO light rail system in
Minneapolis, Minnesota Minneapolis () is the largest city in Minnesota, United States, and the county seat of Hennepin County. The city is abundant in water, with thirteen lakes, wetlands, the Mississippi River, creeks and waterfalls. Minneapolis has its origi ...
, the
Valley Metro Rail Valley Metro Rail (styled as METRO) is a light rail line serving the cities of Phoenix, Tempe, and Mesa in Arizona, USA. The network, which is part of the Valley Metro public transit system, began operations on December 27, 2008. In , the sy ...
in
Phoenix, Arizona Phoenix ( ; nv, Hoozdo; es, Fénix or , yuf-x-wal, Banyà:nyuwá) is the List of capitals in the United States, capital and List of cities and towns in Arizona#List of cities and towns, most populous city of the U.S. state of Arizona, with 1 ...
, and the RTA Streetcar System in
New Orleans New Orleans ( , ,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.


Europe

In some European countries and
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
, 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. The
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 ...
uses a distinctive "negenoog" (nine-eyed) design shown on the top row of the diagram; bottom row signals are used in
Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to ...
, 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 "yellow"), and "stop" (equal to "red").


Asia Pacific

In Japan, tram signals are under the regular vehicle signal; however, the colour of the signal intended for trams is orange. In Sweden, All signals use white lighting and special symbols ("S", "–" and an arrow) to distinguish them from regular signals. 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. File:HK Causeway Bay tram traffic lights Aug-2017.jpg, T signal (trams) in Hong Kong File:Genèva tram signal 00678 729x1296.jpg, Tram signals, Geneva File:Karlsruhe Ebertstr-Karlstr Tramampeln.jpg, Bus and tram signals in
Karlsruhe Karlsruhe ( , , ; South Franconian: ''Kallsruh'') is the third-largest city of the German state (''Land'') of Baden-Württemberg after its capital of Stuttgart and Mannheim, and the 22nd-largest city in the nation, with 308,436 inhabitants. ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
File:Public traffic signal.jpg, Swedish tram signal File:Chinatown Spadina Toronto.JPG, Toronto 'Spadina' signals (black signals for transport) File:Т-образный светофор.JPG, Tram signal showing 'stop' in Moscow, Russia File:Newport, traffic lights for buses on Queensway - geograph.org.uk - 2816844.jpg, A bus traffic light in Newport, United Kingdom


Preemption and priority

Some regions have signals that are interruptible, giving priority to special traffic, usually
emergency vehicle An emergency vehicle is a vehicle used by emergency services. Emergency vehicles typically have specialized emergency lighting and vehicle equipment that allow emergency services to reach calls for service in a timely manner, transport equipment ...
s such as fire apparatus, ambulances, and police squad cars. Most of the systems operate with small transmitters that send radio waves,
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
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.


Turning vehicles


Turn on red

Some jurisdictions, particularly in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
, permit drivers to make a kerb-to-kerb turn (i.e. not crossing other traffic streams) at a red light, provided they first come to a complete stop and give way to other traffic and pedestrians. The rule has been criticised for endangering pedestrians, and some highway authorities have banned turning on red at specific junctions.


Green arrow

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. Generally, a green phase is illuminated at the beginning of the green phase (a "leading turn") or at the end of the green phase (a "lagging turn"). An 'indicative arrow' may be displayed alongside a green light. This indicates to drivers that oncoming traffic is stopped, such that they do not need to give way to that traffic when turning across it. As right-turning traffic (left-side drive) or left-turning traffic (right-side drive) does not normally have priority, this arrow is used to allow turning traffic to clear before the next phase begins. Some variations exist on this set up: * One version is a horizontal bar with five lights – the green and yellow arrows are located between the standard green and yellow lights. A vertical five-light bar holds the arrows underneath the standard green light (in this arrangement, the amber arrow is sometimes omitted, leaving only the green arrow below the steady green light, or possibly an LED-based device capable of showing both green and amber arrows within a single lamp housing). * Some newer LED turn arrows seen in parts of Canada are capable of multicoloured animation. Such lights will often display a flashing and animated green or yellow arrow when the dedicated turn is allowed but then transform into a red arrow on a white background with a red line through it, emphasising that the turn is no longer allowed. These lights will also often have the words "no turn" displayed, or an explanatory reason why the turn is not allowed, such as "train" in the case of a rail or light rail crossing. * A third type is known as a "doghouse" or "cluster head" – a vertical column with the two normal lights is on the right side of the signal, a vertical column with the two arrows is located on the left, and the normal red signal is in the middle above the two columns. Cluster signals in Australia and
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 coun ...
use six signals, the sixth being a red arrow that can operate separately from the standard red light. * In a fourth type, sometimes seen at intersections in
Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
and
Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirte ...
, Canada, there is no dedicated left-turn lamp per se. Instead, the normal green lamp flashes rapidly, indicating permission to go straight as well as make a left turn in front of opposing traffic, which is being held by a steady red lamp. (This "advance green," or flashing green can be somewhat startling and confusing to drivers not familiar with this system. This also can cause confusion amongst visitors to British Columbia, where a flashing green signal denotes a pedestrian-controlled crosswalk. For this reason, Ontario is phasing out the use of flashing green signals and instead replacing them with arrows.)


Flashing yellow

Flashing yellow arrows typically indicate that road users must give way (to other drivers and pedestrians) before making a movement in the direction of the arrow. These are used because they are safer, cause less delay, and are more flexible. Flashing yellow arrows will normally be located below the solid yellow.


Yellow trap

Without an all-red phase, cross-turning traffic may be caught in a yellow trap. When the signal turns 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.


Hook turn

A
hook turn A hook turn (Australian English) or two-stage turn (British English), also known as a Copenhagen Left (in reference to cyclists specifically), is a road cycling manoeuvre or a motor vehicle traffic-control mechanism in which vehicles that would ...
, or two-stage turn, is generally used to allow lighter vehicles such as cycles or motorcycles to turn across oncoming traffic. Such vehicles when permitted can move to the nearside of the junction and position themselves in front of side road traffic, waiting for the side road traffic to gain a green signal before completing the turn. In Australia, such turns were the standard right turn until the 1950s. Hook turns remaining in Australia are generally in the Melbourne central city area to ensure cars do not wait on centre-lane tram tracks and delay trams.


Variable lane control

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 Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * Tidal (servic ...
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. In the US, most notably the Southeastern, there often is a "continuous-flow" lane. This lane is protected by a single, constant-green arrow pointing down at the lane(s) permitting the continuous flow of traffic, without regard to the condition of signals for other lanes or cross streets. Continuous lanes are restricted in that vehicles turning from a side street may not cross over the double white line to enter the continuous lane, and no lane changes are permitted to the continuous lane from an adjacent lane or from the continuous lane to an adjacent lane until the double white line has been passed. Some continuous lanes are protected by a raised curb located between the continuous lane and a normal traffic lane, with white and/or amber reflective paint or tape, prohibiting turning or adjacent traffic from entering the lane. Continuous-flow traffic lanes are found only at "T" intersections where there is no side street or driveway entrance on the right side of the main thoroughfare; additionally, no pedestrians are permitted to cross the main thoroughfare at intersections with a continuous-flow lane, although crossing at the side street may be permitted. Intersections with continuous-flow lanes will be posted with a white regulatory sign approximately before the intersection with the phrase, "right lane continuous traffic," or other, similar, wording. If the arrow is extinguished for any reason, whether by malfunction or design, traffic through the continuous lane will revert to the normal traffic pattern for adjacent lanes, except that turning or moving into or out of the restricted lane is still prohibited.


Inactive lights

Traffic light failure in most jurisdictions in Australia and countries in Europe must be handled by drivers as a priority-to-the-right intersection, or an all-way stop elsewhere, pending the arrival of a police officer to direct traffic. In
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, traffic lights may have additional
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 ...
signs mounted above, below or next to the traffic lights; these take effect when the lights are no longer active or are flashing amber. A flashing amber traffic light usually indicates you have a yield or
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 ...
as a redundant sign, while a turned-off traffic light usually indicates you have the right-of-way. In the UK and parts of North America, drivers simply treat the junction as being uncontrolled when traffic lights fail, giving way as appropriate, unless a police officer is present. In much of the United States failed traffic signals must be treated as
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 ...
intersections. In the US, traffic lights inactive at night time emit an amber-coloured flashing signal in directions owing priority while the intersecting street emits a flashing red light, requiring drivers to stop before proceeding.


Technology


Optics and lighting

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.


Programmable visibility signals

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. These signals were first developed by the 3M Company in the late 1960s and were popular in the late 1970s as traffic density increased. 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. Today, McCain Traffic Systems is the only U.S.-based manufacturer producing optically programmable traffic signals similar to the 3M model. 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.


Conventional lighting systems

Conventional traffic signal lighting, still common in some areas, uses a standard light bulb. Typically, a 67, 69, or 115-watt medium-base (household lamp in the US) light bulb provides the illumination. 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. Crouse-Hinds is one notable company for this practice. In the 1930s throughout the 1950s, they used a beaded prismatic lens with a "smiley" pattern embossed into the bottom of each lens.


Light design

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. For example, these "12-8-8" (along with 8-8-8) lights are standard in most jurisdictions in Ontario, Manitoba, and British Columbia (that, is, the red light is 12 and others 8, making the red more prominent). 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 very 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.


Technological advancements

With technologies in developed countries continuing to advance, there is now an increasing move to develop and implement
smart traffic light Smart traffic lights or Intelligent traffic lights are a vehicle traffic control system that combines traditional traffic lights with an array of sensors and artificial intelligence to intelligently route vehicle and pedestrian traffic. They can ...
s on the roads. These are systems that adapt to information that is received from a central computer about the position, speed, and direction of vehicles. They try to communicate with cars to alert drivers of impending light changes and reduce motorists' waiting time considerably. Trials are currently being conducted for the implementation of these advanced traffic lights but there are still many hurdles to widespread use that need to be addressed; one of which is the fact that few cars yet have the required systems to communicate with these lights.


Control and coordination


Detection

In some instances, small vehicles such as motorcycles, scooters, and bicycles may not be detected, leaving the traffic light controller unaware of their presence. When this occurs, the small vehicle may fail to receive the right of way when the traffic light controller skips their phase, such as at traffic lights that are programmed to remain green for the main street and to only service minor movements, such as the side street or the main street left turn lane, on an as-needed basis when there is demand. For example, small vehicles may not be detected by an induction loop sensor, such as one whose sensitivity has been set too high in an attempt to avoid false triggers. While a typical motor vehicle has a sufficient mass of metal such as steel that interacts with the sensor's magnetic field, motorcycles and scooters have much less mass than cars, and bicycles may not even be constructed with metal. 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.


Mounting

There are significant differences from place to place in how traffic lights are mounted or positioned so that they are visible to drivers. Depending upon the location, traffic lights may be mounted on poles situated on street corners, hung from horizontal poles or wires strung over the roadway, or installed within large horizontal gantries that extend out from the corner and over the right-of-way. In the last case, such poles or gantries often have a lit sign with the name of the cross-street. File:Fort Worth, TX Traffic Light - Berry Street and Evans Avenue.JPG, An example of a wire-mounted traffic light in
Fort Worth, Texas Fort Worth is the List of cities in Texas by population, fifth-largest city in the U.S. state of Texas and the List of United States cities by population, 13th-largest city in the United States. It is the county seat of Tarrant County, Texas, T ...
File:9th-food.jpg, A typical traffic light on Ninth Avenue in
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
. Note that the traffic light gantry is of a guy-wire masted style, which is unique to New York City. File:Silver Line buses on Washington Street, May 2012.jpg, A vertically mounted traffic light in
Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...
File:2014-12-20 14 49 17 Horizontally-mounted traffic light at the intersection of Calhoun Street (Mercer County Route 653) and Spring Street in Trenton, New Jersey.JPG, Example of horizontally mounted traffic light in Trenton,
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delawa ...
File:Stampede Traffic Signal.JPG, Horizontally mounted traffic lights in
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Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...
File:Traffic light at megasection.jpg, A bulky tubular metal structure. Not only is the intersection very large, but due to its location on
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
's east coast, the traffic lights must be hurricane resistant. File:AbingtonUpper Dublin border Fitzwatertown and North Hills traffic signal setup, Eagle brand traffic signals on angled mast-arms, installed July 1969.png, Angled mast-arms, which were frequently used in the state of
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during the 1960s and 1970s File:KOP traffic light.jpg, Three horizontally mounted traffic lights for visibility under a bridge in King of Prussia, Pennsylvania. Pennsylvania typically mounts traffic lights vertically. File:Cincinnati 396.JPG, In downtown
Cincinnati Cincinnati ( ) is a city in the U.S. state of Ohio and the county seat of Hamilton County. Settled in 1788, the city is located at the northern side of the confluence of the Licking and Ohio rivers, the latter of which marks the state line w ...
, traffic lights are mounted horizontally on gantries alongside illuminated traffic signs.
In some locations, lights are mounted with their multiple faces arranged horizontally, often with supplemental vertical signals on the side, while other locations use vertical signals almost exclusively. Horizontal signals have consistent orientation, like their vertical counterparts. Often, supplemental curb pedestal mounts, intended to support a signal for a different approach road, are used when primary signals are partially obscured due to structures such as overpasses, approaches around a building that obscures the primary signal mountings, and unusual approach geometry. In Florida, horizontal signals mounted on poles, known as "mast arms", are in wide use due to their lower wind profile, important for minimizing
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damage. In areas where wind-load is not as much of a concern as ice-load, such as
Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rock ...
or
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over t ...
, the lights are mounted vertically to reduce the accumulation of ice or snow over the surface of the signal heads. In a few countries such as
Mexico Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...
and a few provinces in Canada such as
New Brunswick New Brunswick (french: Nouveau-Brunswick, , locally ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. It is the only province with both English and ...
, most traffic signals are mounted horizontally. Traffic signals in most areas of Europe are located at the stop line on the same side of the intersection as the approaching traffic (there being both right- and left-hand traffic) and are often mounted overhead as well as on side of the road. At particularly busy junctions for freight, higher lights may be mounted specifically for trucks. The stop line alignment is done to prevent vehicles from blocking any crosswalk and allow for better pedestrian traffic flow. There may also be a special area a few meters in advance of the stop line where cyclists may legally wait but not motor vehicles; this
advanced stop line An advanced stop line (ASL), also called advanced stop box or bike box, is a type of road marking at signalised road junctions allowing certain types of vehicle a head start when the traffic signal changes from red to green. Advanced stop lines ...
is often painted with a different road surface with greater friction and high colour, both for the benefit of cyclists and for other vehicles. The traffic lights are mounted so that cyclists can still see them. In Spain, the mounted traffic lights on the far side of the intersection are meant for the traffic that exits the intersection in that particular direction. This is often done due to the pedestrian crossings, so that traffic has to wait if they get a red light. These intersections also come with a stop line in the exit area of the intersection. In North America, there is often a pole-mounted signal on the same side of the intersection, but additional pole-mounted and overhead signals are usually mounted on the far side of the intersection for better visibility. Most traffic lights are mounted that way in the Western United States and Canada. In Ontario, traffic lights are almost always mounted on the far side of the intersection with poles. In some areas of the United States, signals facing in up to four directions are hung directly over the intersection on a wire strung diagonally over the intersection (once common in
Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and t ...
), or the signal faces traffic in one direction, still hung by wires (but the wire is strung horizontally between two adjacent corners of the intersection). This is common in the Southern and Eastern United States. Dummy lights are traffic signs located in the centre of a junction, which operate on a fixed cycle. These have generally been decommissioned due to safety concerns; however, a number remain due to historic value. In other countries including the
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,
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
,
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 coun ...
,
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
, and
Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon () or the Lebanese Republic, is a country in Western Asia. It is located between Syria to the north and east and Israel to the south, while Cyprus lie ...
, traffic lights are mounted at the stop line before the intersection and also after the intersection. Some busy intersections have an overhead traffic light for heavy vehicles and vehicles further away.


Effects

Traffic lights can have both positive and negative effects on traffic safety and traffic flow.


Traffic flow

Drivers spend on average around 2% of journey time passing through signalised junctions. 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 Hans Monderman (19 November 1945 – 7 January 2008) was a Dutch road traffic engineer and innovator. He was recognised for radically challenging the criteria used to evaluate engineering solutions for street design. His work compelled tra ...
, the innovative Dutch traffic engineer, and pioneer of
shared space Shared space is an urban design approach that minimises the segregation between modes of road user. This is done by removing features such as kerbs, road surface markings, traffic signs, and traffic lights. Hans Monderman and others have sugg ...
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."


Pollution

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.


Accidents

The separation of conflicting streams of traffic in time can reduce the chances of right-angle collisions by turning traffic and cross traffic, but they can increase the frequency of rear-end crashes by up to 50%.National Cooperative Highway Research Program, Crash Reduction Factors for Traffic Engineering and Intelligent Transportation System (ITS) Improvements: State-of-Knowledge Report, November 2005, Table 3 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 Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Since ...
, 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 traffic lights had been erected in the 1960s because of since-resolved protests over traffic. By 1992, over 800 traffic lights had been removed at 426 intersections, and the number of crashes at these intersections dropped by 60%.


Justification

Criteria have been developed to help ensure that new traffic lights are installed only where they will do more good than harm and to justify the removal of existing traffic lights where they are not warranted. They are most often placed on arterial roads at intersections with either another arterial road or a collector road, or on an expressway where an interchange is not warranted. In some situations, traffic signals can also be found on collector roads in busy settings.


United States

In the United States, the criteria for installation of a traffic control signal are prescribed by the Manual on Uniform Traffic Control Devices (MUTCD), which defines the criteria in nine ''warrants'': * Eight-hour vehicular volume. Traffic volume must exceed prescribed minima for eight hours of an average weekday. * Four-hour vehicular volume. Traffic volume must exceed prescribed minima for four hours of an average weekday. * Peak hour volume or delay. This is applied only in unusual cases, such as
office park A business park or office park is a designated area of land in which many office buildings are grouped together. These types of developments are often located in suburban areas where land and building costs are more affordable, and are typically ...
s, industrial complexes, and park and ride lots that attract or discharge large numbers of vehicles in a short time, and for a minimum of one hour of an average weekday. The side road traffic suffers undue delays when entering or crossing the major street. * Pedestrian volume. If the traffic volume on a major street is so heavy that pedestrians experience excessive delays in attempting to cross it. * School crossing. If the traffic density at school crossing times exceeds one per minute which is considered to provide too few gaps in the traffic for children to safely cross the street. * Coordinated signal system. For places where adjacent traffic control signals do not keep traffic grouped together efficiently. * Crash experience. The volumes in the eight- and four-hour warrants may be reduced if five or more right-angle and cross traffic turn collisions have happened at the intersection in a twelve-month period. * Roadway network. Installing a traffic control signal at some intersections might be justified to encourage concentration and organization of traffic flow on a roadway network. * Intersection near a grade crossing. A traffic control signal is often justified at an intersection near a railroad crossing, in order to provide a preemption sequence to allow traffic queued up on the tracks an opportunity to clear the tracks before the train arrives. An intersection is usually required to meet one or more of these warrants before a signal is installed. However, meeting one or more warrants does not require the installation of a traffic signal, it only suggests that they may be suitable. It could be that a roundabout would work better. There may be other unconsidered conditions that lead traffic engineers to conclude that a signal is undesirable. For example, it may be decided not to install a signal at an intersection if traffic stopped by it will back up and block another, more heavily trafficked intersection. Also, if a signal meets only the peak hour warrant, the advantages during that time may not outweigh the disadvantages during the rest of the day.


Legal issues

In virtually all jurisdictions in which they are used, it is an offence for motorists (and other road users) to disobey traffic control devices, such as traffic lights.


Blocking a traffic light junction

In some jurisdictions (such as
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
), there are ordinances or by-laws against "
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 ...
ing". A motorist entering an intersection (even if on a green light) but unable to proceed and who gets stranded in the intersection (when traffic ahead fails to proceed), and who remains after the light turns red (thus blocking traffic from other directions) may be cited. The definition of the intersection area is a square where the two streets overlap marked by the inner lines of each crosswalk. (Occupying the space inside the crosswalk lines is itself a traffic infraction, but different from gridlocking.) This gives meaning to the anti-gridlock slogan "don't block the box". This is sometimes used as a justification for making a turn across the opposing travel lanes on a red light at a busy intersection, by pulling partway into the intersection at a green light waiting to perform the turn, and, if oncoming traffic is not abated before the light changes to red, proceeding to turn once the light has turned red and opposing traffic has stopped. This means that at busy junctions without a protected green arrow for turning traffic, one turns after the light turns red. This maneuver is commonly referred to as "occupying the intersection" or "being legally allowed to complete one's turn". In some jurisdictions, including most American states, a vehicle already in the intersection when the light turns red legally has the right of way, and vehicles who have green must yield to the vehicle in the intersection. In Sackville, New Brunswick, it is customary for through traffic to voluntarily yield to the first oncoming left-turning vehicle to allow it to perform a "
Pittsburgh left The Pittsburgh left is a colloquial term for the driving practice of the first left-turning vehicle taking precedence over vehicles going straight through an intersection, associated with the Pittsburgh, Pennsylvania, area. In other locales, the ...
" manoeuvre. This is similar to a
hook turn A hook turn (Australian English) or two-stage turn (British English), also known as a Copenhagen Left (in reference to cyclists specifically), is a road cycling manoeuvre or a motor vehicle traffic-control mechanism in which vehicles that would ...
performed in Melbourne, Australia, which is legal at signed intersections. Enforcement of traffic lights is done in one of several ways: * by police officers observing traffic, and issuing citations to motorists who violate the signal * as a result of an accident investigation, if it is determined that one or more motorists ran the red lighteven if the incident was not observed by a police officer * with red light cameras


Red light running

Red light running occurs when a motorist enters a junction any time after the signal light turns red unless a legal turn on red manoeuvre is completed. A US national survey in 2019 found that 86% of drivers thought it was very dangerous to run a red light at speed, but 31% reported that they had done so in the past 30 days.


Reasons and impacts

Common reasons for red light running include inattentive driving, following an oversized vehicle, or during inclement weather. Drivers are more likely to run red lights during peak traffic hours or if the signal is on a downward slope.
Uber Uber Technologies, Inc. (Uber), based in San Francisco, provides mobility as a service, ride-hailing (allowing users to book a car and driver to transport them in a way similar to a taxi), food delivery ( Uber Eats and Postmates), pa ...
had to apologise in 2016 after a self-driving Uber vehicle ran a red light "due to human error" in San Francisco. Red light runners involved in multiple-vehicle crashes are more likely male, younger, involved in prior crashes, or have alcohol-impaired driving convictions. According to the IIHS Insurance Institute for Highway Safety, every year red light running causes hundreds of deaths, thousands of injuries, and hundreds of millions of dollars in related costs. In Spring 2015,
Hunter College Hunter College is a public university in New York City. It is one of the constituent colleges of the City University of New York and offers studies in more than one hundred undergraduate and postgraduate fields across five schools. It also admin ...
in New York City completed an observational study of red light running, the first of its kind. The conclusion, after monitoring 3,259 vehicles at 50 intersections over a period of days around the 5
boroughs A borough is an administrative division in various English-speaking countries. In principle, the term ''borough'' designates a self-governing walled town, although in practice, official use of the term varies widely. History In the Middle A ...
, found that almost 10% of vehicles and 15% of taxis ran the red light, amounting to nearly 400,000 red lights run every single day. ''Source: IIHS''


Mitigations

Red light running can be deterred through enforcement or engineering strategies. It is normally illegal and may incur a fine, demerit points, or a stricter sentence. As of 2021, Norway has the highest fine in Europe for red light running at €756 equivalent. The US
Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program ...
recommends that engineers: * improve signal visibility (better signal placement, increased signal size or improved line of sight); * improve signal conspicuity (to better capture the motorist's attention); * increase the likelihood of stopping (with signal head signs, advance-warning flashers or rumble strips); and * address intentional violations (through signal optimisation, properly timed yellow-change intervals, and all-red clearance intervals). After the Hunter College study, New York City Mayor Bill de Blasio launched a Vision Zero plan to reduce vehicular and pedestrian fatalities. The
New York City Police Department The New York City Police Department (NYPD), officially the City of New York Police Department, established on May 23, 1845, is the primary municipal law enforcement Law enforcement is the activity of some members of government who act i ...
's 2014 TrafficStat report showed 33,577 red light tickets for 2013, which is a 126% increase in the number of failure-to-yield summonses and red-light running violations.


Red light cameras

In some countries, red light cameras are used for either the driver or the vehicle's owner. An automated camera is connected to the triggering mechanism for the corresponding traffic light, which is programmed to photograph a vehicle and driver crossing against the light. Either the driver or the vehicle's owner (depending on the locale) are fined for the violation. In some jurisdictions, including the United States and Italy, private companies have been contracted to operate traffic-related cameras and receive a portion of the resulting revenues. In some cases, red light cameras have been abused by local governments, where vehicle operators have been fined as a result of traffic systems that have been improperly modified. Despite the fact that cameras can reduce the number of crashes, it has been proven that at these intersections drivers tended to react quicker to an amber light change when stopping. The consequence of this change could be a slight decline in the intersection capacity. Red light cameras in New South Wales, Australia, are activated only if a motorist enters an intersection 0.3 seconds after the light has turned red.


Yellow lights

In some jurisdictions, yellow light running may also be illegal, unless a driver cannot stop before the stop line safely. For example, this rule is in place in states within Australia, Russia (which also has a flashing green phase and possibly countdown timers to warn drivers of a yellow phase), and the UK. The '' Amber Gambler Twins'' is one of many public interest films trying to change the public's behaviour regarding the running of yellow lights.


Confirmation lights

Another way police officers have begun to combat red light runners is with blue or white ''Confirmation Lights''. These lights can be seen from any angle in an intersection and are typically utilised by emergency responders who actuate traffic signal preemption devices to verify that other motorists are facing a red signal. However, confirmation lights also assist officers – who do not have to have a line of sight with a red light – to catch vehicles illegally entering an intersection. They are only lit when the red light on the same signal head is on. Some intersections will also have multiple confirmation lights for a single direction of travel if there are different signals for different directions. These lights are separate from the main ones, often protruding above or below the main traffic light, and are much smaller than a standard light to help avoid confusion. In the
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 ...
, many red traffic signals can be seen from the side via a small bulbous window, indicating to drivers (and police officers) whether the signal in the crossing direction is actually red or not, by simply leaking out some of the red light through the side of the traffic signal. This has gradually become less common as traditional incandescent signals are replaced by LED signals, while increasingly red light cameras are used to detect driving-through-red violations.


Light timing length

The length of yellow lights can differ, for example in many places the length of a yellow light is usually four or five seconds, but elsewhere it may be as little as three, considerably reducing the time for reaction. It is typical for these times to vary according to the set speed limit, with longer times for higher limits. In the U.S. state of Georgia, an amber light must be lit one second for every of the posted speed limit. For intersections with red light cameras, one extra second must be added. In
Colorado Springs, Colorado Colorado Springs is a home rule municipality in, and the county seat of, El Paso County, Colorado, United States. It is the largest city in El Paso County, with a population of 478,961 at the 2020 United States Census, a 15.02% increase since ...
, amber lights at numerous intersections have been noted with durations of approximately two seconds. In the United States, there is a recommended federal safety minimum of three seconds for amber lights. The time between when a red light is displayed and when a cross street is given a green light is usually based on the physical size of the intersection. This intervening period is called the "all-red time". A typical all-red time is two seconds to allow cars to clear the intersection. In a wider intersection, such as a four-lane road or highway intersection, the all-red time may be as much as five seconds, allowing drivers who could not or would not stop at the amber light enough time to clear the intersection without causing a collision. Two exceptions are in New Westminster, British Columbia, Canada, and
Winnipeg, Manitoba Winnipeg () is the capital and largest city of the province of Manitoba in Canada. It is centred on the confluence of the Red and Assiniboine rivers, near the longitudinal centre of North America. , Winnipeg had a city population of 749,60 ...
, Canada, where there is no all-red time. The change is instantaneous, due to the nature of the older relay-operated signals. It is also the case in Montreal, Quebec, Canada.


In other contexts

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 macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
user interface, and in pieces of artwork, particularly the Traffic Light tree in London, UK.


Racing

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 Formula One (also known as Formula 1 or F1) is the highest class of international racing for open-wheel single-seater formula racing cars sanctioned by the Fédération Internationale de l'Automobile (FIA). The World Drivers' Championship, ...
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 Adrian Sutil (; born 11 January 1983) is a German-Uruguayan racing driver who raced in Formula One for seven seasons: from 2007–2011, then 2013– 2014. He drove for the Spyker F1 Team, Force India F1 Team and the Sauber F1 Team. He was also ...
, 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.


As a rating mechanism

The colours red, yellow, 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.


Gallery

File:LED Traffic Light.jpg, LED traffic light (using cap visors) File:Traffic light red green for parking lot.jpg, Traffic light with only red and green lights in the entrance of a parking lot File:Portable LED traffic light.jpg, Temporary LED traffic lights with sensor in Australia File:Traffic Lights onto Wheatley Hall Road - geograph.org.uk - 699304.jpg, Traffic lights
South Yorkshire South Yorkshire is a ceremonial and metropolitan county in the Yorkshire and Humber Region of England. The county has four council areas which are the cities of Doncaster and Sheffield as well as the boroughs of Barnsley and Rotherham. ...
,
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 ...
File:Temporary traffic light.JPG, Temporary traffic light in the United Kingdom File:Red Man, Downpatrick, March 2011.JPG, Pelican Crossing "red man" signal, Market Street, Downpatrick, County Down,
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 ...
File:Green man uk.jpg, Pelican Crossing "green man" signal,
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 ...
File:TrafficLights-HagerstownMD.jpg, Traffic light in a small intersection in Hagerstown, Maryland (using tunnel visors) File:Cincinnati 396.JPG, Example of traffic signals mounted on gantries in downtown
Cincinnati, Ohio Cincinnati ( ) is a city in the U.S. state of Ohio and the county seat of Hamilton County. Settled in 1788, the city is located at the northern side of the confluence of the Licking and Ohio rivers, the latter of which marks the state line w ...
, and integrated with street signage File:Michigan left lighted sign.jpg, Typical set of traffic lights in
East Lansing, Michigan East Lansing is a city in the U.S. state of Michigan. Most of the city lies within Ingham County with a smaller portion extending north into Clinton County. At the 2020 Census the population was 47,741. Located directly east of the state capital ...
File:Main Street and Lewis Street - Monroe, WA.jpg, Typical set of traffic lights at the intersection of Main Street and Lewis Street (Washington State Route 203) in downtown
Monroe, Washington Monroe is a city in Snohomish County, Washington, United States. It is located at the confluence of the Skykomish, Snohomish, and Snoqualmie rivers near the Cascade foothills, about northeast of Seattle. Monroe's population was 19,699 as o ...
File:Stevens Creek Blvd traffic light.jpg, Typical example of traffic lights mounted on a wide street in California File:Trafficsignalwide.jpg, One example of traffic lights on a suburban street in
Santa Clarita, California Santa Clarita (; Spanish for "Little St. Clare") is a city in northwestern Los Angeles County in the U.S. state of California. With a 2020 census population of 228,673, it is the third-largest city by population in Los Angeles County, the 17 ...
File:Led traffic lights.jpg, LED traffic lights in Örnsköldsvik, Sweden File:Semaforoencendido.jpg, Typical set of traffic lights in Spain File:SyracuseTipperaryLight.jpg, The green on top light in Tipperary Hill, Syracuse, New York File:Pedestrian LED Traffic Light NYC.jpg, LED pedestrian signal in New York City File:Traffic light, Ashgabat.jpg, Traffic light in Ashgabat, Turkmenistan File:Marshalite traffic signal, Melbourne Museum.jpg, A
Marshalite The Marshalite was a form of rotary traffic signal that was designed in 1936 by an Australian Charles Marshall (engineer), Charles Marshall (1864 - Dunedin, New Zealand - 3 April 1953, Mornington, Victoria, Australia), founder of the Fitzroy, Vic ...
traffic signal, as formerly installed at various intersections in
Melbourne Melbourne ( ; Boonwurrung/ Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a metro ...
, Australia, indicating how much time remained before a signal change File:01054jfBarangays East Rembo Buting Pasig J. P. Rizal Extension Makati Cityfvf 20.jpg, East Rembo Buting Intersection traffic light near Kalayaan Ave File:U-turn traffic light.jpg, A U-turn traffic light in
Lake Buena Vista, Florida Lake Buena Vista () is a city in Orange County, Florida, United States. It is mostly known for being the mailing address for Walt Disney World—although almost all of the resort facilities, including all four theme parks, are physically located ...
File:Traffic lights in Turin 2021.jpg, These traffic lights in
Turin Turin ( , Piedmontese language, Piedmontese: ; it, Torino ) is a city and an important business and cultural centre in Northern Italy. It is the capital city of Piedmont and of the Metropolitan City of Turin, and was the first Italian capital ...
,
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
, are not up to the Italian traffic code. Since 1993, the green and amber lights should light up separately.


In Unicode

In
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...
, the symbol for is HORIZONTAL TRAFFIC LIGHT and is VERTICAL TRAFFIC LIGHT.


See also

* Ampelmännchen *
Glossary of road transport terms Terminology related to road transport—the transport of passengers or goods on paved (or otherwise improved) routes between places—is diverse, with variation between dialects of English. There may also be regional differences within a single co ...
* Induction loop * Lane control lights *
Level crossing A level crossing is an intersection where a railway line crosses a road, path, or (in rare situations) airport runway, at the same level, as opposed to the railway line crossing over or under using an overpass or tunnel. The term a ...
* North American railroad signals, rail equivalent * Pedestrian crossing *
Railway signal A railway signal is a visual display device that conveys instructions or provides warning of instructions regarding the driver’s authority to proceed. The driver interprets the signal's indication and acts accordingly. Typically, a signal mi ...
, another rail equivalent *
Ramp meter A ramp meter, ramp signal, or metering light is a device, usually a basic traffic light or a two-section signal light (red and green only, no yellow) together with a signal controller, that regulates the flow of traffic entering freeways accordi ...
* Stack light, used in industrial process control *
Traffic light coalition In German politics, a traffic light coalition (german: Ampelkoalition) is a coalition government of the Social Democratic Party of Germany (SPD), the Free Democratic Party (FDP) and Alliance 90/The Greens. It is named after the parties' tradi ...
*
Traffic light control and coordination The normal function of traffic lights requires more than sight control and coordination to ensure that traffic and pedestrians move as smoothly, and safely as possible. A variety of different control systems are used to accomplish this, ranging fr ...
* Traffic-light signalling and operation * Traffic optimization * Traffic robots in Kinshasa * Slow Children At Play *
Smart traffic light Smart traffic lights or Intelligent traffic lights are a vehicle traffic control system that combines traditional traffic lights with an array of sensors and artificial intelligence to intelligently route vehicle and pedestrian traffic. They can ...
* Yellow trap


Notes


References


Citations

* 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

Retrieved 30 September 2008. *


External links



* ttp://projects.kittelson.com/pplt/displays2.htm Animations of various US signal phasings
SCATSSydney Coordinated Adaptive Traffic System

Safety Evaluation of Converting Traffic Signals from Incandescent to Light-emitting Diodes: Summary Report
Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program ...

Safety Evaluation of Discontinuing Late-night Flash Operations at Signalized Intersections: Summary Report
Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program ...

Traffic signals, 1922
digitized NYPD photograph from the Lloyd Sealy Library Digital Collections {{Authority control * 1868 introductions Street furniture Traffic law Articles containing video clips History of road transport Pedestrian crossings