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This article is about lights used for signalling. For other uses, see Traffic light (disambiguation)
"Stoplight" redirects here. For other uses, see Stoplight (disambiguation)
An LED 50-watt traffic light in Portsmouth, United Kingdom
Traffic lights, traffic signals, or stoplights &#; also known as robots in South Africa[1][2] and Namibia &#; are signaling devices positioned at road intersections, pedestrian crossings, and other locations in order to control the flow of traffic.[3]
Traffic lights normally consist of three signals, transmitting meaningful information to road users through colours and symbols, including arrows and bicycles. The regular traffic light colours are red, yellow (also known as amber), and green arranged vertically or horizontally in that order. Although this is internationally standardised,[4] variations in traffic light sequences and laws exist on national and local scales.[5]
Traffic lights were first introduced in December on Parliament Square in London to reduce the need for police officers to control traffic.[6] Since then, electricity and computerised control has advanced traffic light technology and increased intersection capacity. The system is also used for other purposes, including the control of pedestrian movements, variable lane control (such as tidal flow systems or smart motorways), and railway level crossings.
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The first system of traffic signals, which was a semaphore traffic signal, was installed as a way to replace police officer control of vehicular traffic outside the Houses of Parliament in London on 9 December . This system exploded on 2 January and was thus taken down. But, this early traffic signal led to other parts of the world implementing similar traffic signal systems. 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. These traffic signals controlled by a traffic officer who would change the commands on this signal to direct traffic.
In , the first electric traffic light was developed by Lester Wire, a policeman in Salt Lake City, Utah.[9] It was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio.[11][12] The first four-way, three-colour traffic light was created by William Potts in Detroit, Michigan in .[13] His design was the first to include an amber 'caution' light along with red and green lights.[14] Potts was Superintendent of Signals for the Police Department of Detroit. He installed automatic four-way, three-colour traffic lights in 15 towers across Detroit in .[15][14][13] By , traffic towers were beginning to be controlled by automatic timers more widely. The main advantage of the use of the timer was that it saved cities money by replacing traffic officers. The city of New York was able to reassign all but 500 of its 6,000 officers working on the traffic squad, saving the city $12,500,000.
In , Garrett Morgan patented a design of a manually operated three-way traffic light with moving arms.[17]
The control of traffic lights made a big turn with the rise of computers in America in the s. One of the best historical examples of computerized control of lights was in Denver in . In , the city of Toronto was the first to use more advanced computers that were better at vehicle detection. The computers maintained control over 159 signals in the cities through lines.
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Traffic lights can have several additional lights for filter turns or bus lanes. Road crossing of A970 with Sumburgh Airport's runway in Shetland. The movable barrier closes when aircraft land or take off. Horizontally-mounted signals in JapanA set of lights, known as a signal head,[19]:&#;3.2.4&#; may have one, two, three, or more aspects. The most common signal type has three aspects facing the oncoming traffic: red on top, amber (yellow) below, and green below that. Additional aspects may be fitted to the signal, usually to indicate specific restrictions or filter movements.
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The Vienna Convention on Road Signs and Signals Chapter III provides international standards for the setup of traffic signal operations. Not all states have ratified the convention. A three-colour signal head should have three non-flashing lights which are red, amber, and green, either arranged horizontally (on the side opposite to the direction of traffic) or vertically (with red on top). A two-colour signal head may be used in temporary operation and consists of red and green non-flashing lights. In both cases, all lights should be circular or arrow-shaped.[4] Permissible signals for regulating vehicle traffic (other than public transport vehicles) are outlined in Article 23:[4]
Standard meanings for traffic lights internationally (Vienna Convention, Article 23) Light type Meaning Non-flashing Red Traffic may not proceed beyond the stop line, or otherwise enter the intersection Red/Amber The signal is about to change, but the red light rules do apply Amber Traffic may not pass the stop line or enter the intersection, unless it cannot safely stop when the light shows Green Traffic may proceed, unless it would not clear the intersection before the next change of phase Flashing Red Traffic must not pass the stop line at a level crossing, approach to swing bridge or ferry landing stages, emergency vehicles entering the road, or on the approach to low-flying aircraft. In addition, to attract attention in these locations, it is also equipped with additional alarms and voice prompts Amber Traffic may proceed with cautionGreen 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").[19]:&#;3.5&#; Flashing amber 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 amber arrows will normally be located below the solid amber.[20]
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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.[19]:&#;3.5&#; 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").[citation needed] 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.[19]:&#;3.5&#;
Some variations exist on this set up. One version is a horizontal bar with five lights &#; the green and amber arrows are located between the standard green and amber 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).[citation needed] 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 amber 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. [citation needed]
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 use six signals, the sixth being a red arrow that can operate separately from the standard red light.[citation needed] In a fourth type, sometimes seen at intersections in Ontario and Quebec, 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.)[21][22]
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Popular in Vietnam and China, countdown lights are additional lights installed next to (or above or below) the main signal lights. The countdown light is displayed by a countdown number with different colors (usually red, yellow, green), matching the color of the light on. When the light counts to "0" (or 1), the main light color immediately changes. Countdown lights may have zeros in the tens or none, some countdown lights may flash when getting ready to zero. Yellow lights can also have countdown lights, but most lights do not. Usually the countdown light has 2 digits, in case the time of the main light (usually the red light, rarely the green light) is longer than 100 seconds, depending on the type of light, the following possibilities may occur:
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In South Korea, yellow light dilemma zone is not legally recognised. In other words, when yellow light is on, traffic may not pass the stop line or enter the intersection even if cannot safely stop when the light shows. This has been reaffirmed by the ruling of the Supreme Court of Korea in May .[23][24] There are criticisms in South Korea say that this is unrealistic and unreasonable. In addition, this can cause multiple collisions due to sudden braking.
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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.[25] This can also happen when emergency vehicles or railroads preempt normal signal operation. [26] 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.[27][28]
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The United States is not party to the Vienna Convention; rather, the Manual on Uniform Traffic Control Devices (MUTCD) outlines correct operation in that country. In the US, a single signal head may 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, amber, and green vertically (top to bottom) or horizontally (left to right).[29] In the US, a single-aspect flashing amber 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.[29] Flashing red or amber lights, known as intersection control beacons, are used to reinforce stop signs at intersections.[30] The MUTCD specifies the following vehicular signals:[29]
Standard meanings for traffic lights in the United States (MUTCD, Chapter 4) Signal Meaning (steady) Meaning (flashing)In the Canadian province of Quebec 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, amber 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.[31] Japanese traffic signals mostly follow the same rule except that the green "go" signals are referred to as &#; (ao), typically translated as "blue", reflecting a historical change in the Japanese language. As a result, Japanese officials decreed in that the "go" light should be changed to the bluest possible shade of green, bringing the name more in line with the color without violating the international "green means go" rule.[32]
In the UK, normal traffic lights follow this sequence:[33]
A speed sign is a special traffic light, variable traffic sign, or variable-message sign giving drivers a recommended speed to approach the next traffic light in its green phase[34] and avoid a stop due to reaching the intersection when lights are red.[35][a]
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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 or orange man figure or a hand), though other variations exist.[36]
Pedestrian sequences in various countries Country/ies Sequence Notes Australia, New Zealand, Philippines Green man: safe to crossFlashing red man: do not start to cross; if it appears during crossing, then continue to cross if unable to stop safely
Red man: do not cross
Several intersections in Wellington, New Zealand, have alternative green man figures. Eight intersections near Parliament Buildings have silhouettes of suffragette Kate Sheppard,[
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while four intersections along Cuba Street have silhouettes of drag performer and LGBT rights activist Carmen Rupe.[
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China Green: safe to crossRed: do not cross
Amber (steady, after green, before red): continue to cross only if unable to stop safely
Flashing amber: cross with caution (often used in low-traffic crossing or after midnight)
Japan Blue or green man: safe to cross (cyclists may cross or turn left)Flashing blue or green man: do not start to cross; if it appears during crossing, then continue to cross if unable to stop safely
Red standing man: do not cross
Germany, Czechia, Central Europe Green: safe to crossAmber: continue to cross only if unable to stop safely
Flashing amber: cross with caution, obey signage (used when lights are out of order or shut down)
Red: do not cross
Red and amber: do not cross, prepare for green
In Germany, Ampelmännchen pedestrian traffic signals have come to be seen as a nostalgic sign for the former German Democratic Republic.In Germany, the fine for crossing a red light if caught is as of between &#;5 and &#;10.[39]
United Kingdom, Ireland, Hong Kong, Switzerland, Macao Green walking man: safe to crossFlashing green man or no man: do not start to cross (only at mid-block crossings); if it appears during crossing, then continue to cross if unable to stop safely
Red standing man: do not cross
In the United Kingdom, there is no direct offence committed if a pedestrian fails to obey crossing signals and many lights commonly only use two still images &#; a green walking person and a red standing man, this being the general case where the crossing is at a road junction and the pedestrian signals are in combination with those controlling vehicular traffic. United States, Canada, Mexico (Tijuana), Philippines (Makati, Davao) Formerly signals used the text:[
40]
WALK
DONT WALK
Modern version:
White walking man: cross with caution
Flashing orange stophand: do not start to cross; if it appears during crossing, then continue to cross if unable to stop safely
Orange stophand: do not enter the intersection
The U.S. state of Massachusetts allows an unusual indication variation for pedestrian movement. At signalized intersections without separate pedestrian signal heads, the traffic signals may be programmed to turn red in all directions, followed by a steady display of amber lights simultaneously with the red indications. During this red-plus-amber indication, the intersection is closed to vehicular traffic and pedestrians may cross, usually in whatever direction they choose. Israel Red standing man: do not cross; if it appears during crossing, then continue to cross if unable to stop safelyGreen walking man: safe to cross
Traffic light animation (pedestrians, cyclists and traffic) in Ljubljana, SloveniaWhere 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.[19]:&#;c.18&#; 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.[19]:&#;c.18&#; 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 amber signal. The beacon is unlit until a pedestrian pushes the cross button. Then an amber 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 amber traffic light.[41]
The Shibuya Crossing, in Tokyo, is a famous example of a pedestrian scramble with diagonal crossings.Pedestrians are usually incorporated into urban signalised junctions in one of four ways: no facilities, parallel walk, walk with traffic, or all-red stages. 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.[19]:&#;71&#; 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.[42] 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.[19]:&#;72&#;
An all-red stage, also known as a full pedestrian stage, a pedestrian scramble or a Barnes Dance,[b] holds all vehicular traffic at the junction to allow pedestrians time to safely cross without conflict from vehicles. It allows allows the use of diagonal crossings. This may require a longer cycle time and increase pedestrian wait periods, though the latter can be eased by providing two pedestrian stages.[19]:&#;71&#;72&#;
A diagram of a countdown timer in the US stylePedestrian 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.[19][43] Pedestrian countdown timers do not significantly increase or reduce the number of red- and amber-light running drivers. Studies have found that pedestrian countdown timers do significantly improve pedestrian compliance over traditional pedestrian signals; however, results are mixed.[43][44]
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As the 12 to 45% of pedestrian deaths caused by 'pedestrian distraction' has been linked to cell usage,[45] some cities (including Sydney, Seoul, Augsburg, Bodegraven, Aviv, and Singapore) have installed LED strips embedded in the sidewalk before crosswalks to warn distracted pedestrians of immanent pedestrian crossings.[46] This additional signal, which is synchronized with conventional signals, aims to decrease injury rates by telling distracted pedestrians when it is safe to cross the road without them having to lift their head.
Smartphone zombie light in green, close up
Smartphone zombie light in red
Smartphone zombie light in red, close up
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In some jurisdictions such as Australia, pedestrian lights are associated with a sound device, for the benefit of blind and visually impaired pedestrians. These make a slow beeping sound when the pedestrian lights are red and a continuous buzzing or fast beeping sound when the lights are green. In the Australian States of Queensland, New South Wales, Victoria, and Western Australia, the sound is produced in the same unit as the push buttons. In a circle above the button, the sound is produced and can be felt along with a raised arrow that points in the direction to walk.[47] This system of assistive technology is also widely used at busy intersections in Canadian cities. In the United Kingdom, the Puffin crossings and their predecessor, the Pelican crossing, will make a fast beeping sound to indicate that it is safe to cross the road. The beeping sound is disabled during the nighttime so as not to disturb any nearby residents.[48]
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.[49] Some pedestrian crossings in Lithuania make a slow beeping sound indicating that the traffic light is about to turn off.
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Traffic light for a bike lane, NYC An advanced stop line at traffic lights in LiverpoolWhere cycle lanes or cycle tracks exist on the approach to a signal-controlled junction, it must be considered how to incorporate cyclists safely into the junction to reduce conflict between motor vehicles and cyclists.
An advanced stop line can be placed after the stop line at traffic lights. This allows cyclists to position themselves in front of traffic at a red light and get a headstart.[50]
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.[51]
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.[51] UK engineers have innovated on this design through the Cycle Optimised Protected Signals (CYCLOPS) junction, e.g. in Manchester. 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.[52]
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.[53]
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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 (an LED 100-watt typical) coloured light.
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MUTCD specifies a standard vertically oriented signal with either two or three lenses, displaying white lines on a black background.[54]:&#;Fig.8C-3&#;
Some systems use the letter B for buses and T for trams. The METRO light rail system in Minneapolis, Minnesota, the Valley Metro Rail in Phoenix, Arizona, and the RTA Streetcar System in New Orleans use a simplified variant of the Belgian/French system in the respective city's central business district where only the "go" and "stop" configurations are used. A third signal equal to amber is accomplished by flashing the "go" signal.
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In some European countries and Russia, dedicated traffic signals for public transport (tram, as well any that is using a dedicated lane) have four white lights that form the letter T.[citation needed] 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.[55] In Sweden, All signals use white lighting and special symbols ("S", "&#;" and an arrow) to distinguish them from regular signals.
The Netherlands uses a distinctive "negenoog" (nine-eyed) design shown on the top row of the diagram;[56] bottom row signals are used in Belgium, Luxembourg, France, and Germany. The signals mean (from left to right): "go straight ahead", "go left", "go right", "go in any direction" (like the "green" of a normal traffic light), "stop, unless the emergency brake is needed" (equal to "amber"), and "stop" (equal to "red").
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In Japan, tram signals are under the regular vehicle signal; however, the colour of the signal intended for trams is orange. The small light at the top tells the driver when the vehicle's transponder signal is received by the traffic light. In Hong Kong, an amber T-signal is used for trams, in place of the green signal. In addition, at any tramway junction, another set of signals is available to indicate the direction of the tracks. In Australia and New Zealand, a white "B" or "T" sometimes replaces the green light indicating that buses or trams (respectively) have right of way.
T signal (trams) in Hong Kong
Bus and tram signals in Karlsruhe
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Some regions have signals that are interruptible, giving priority to special traffic, usually emergency vehicles such as firefighting apparatus, ambulances, and police cars.[57][58] Most of the systems operate with small transmitters that send radio waves, infrared signals, or strobe light signals that are received by a sensor on or near the traffic lights. Some systems use audio detection, where a certain type of siren must be used and detected by a receiver on the traffic light structure.
Upon activation, the normal traffic light cycle is suspended and replaced by the "preemption sequence": the traffic lights to all approaches to the intersection are switched to "red" with the exception of the light for the vehicle that has triggered the preemption sequence. Sometimes, an additional signal light is placed nearby to indicate to the preempting vehicle that the preempting sequence has been activated and to warn other motorists of the approach of an emergency vehicle. The normal traffic light cycle resumes after the sensor has been passed by the vehicle that triggered the preemption.
In lieu of preemptive mechanisms, in most jurisdictions, emergency vehicles are not required to respect traffic lights. However, emergency vehicles must slow down, proceed cautiously and activate their emergency lights to alert oncoming drivers to the preemption when crossing an intersection against the light.[59][60]
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.
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A staging diagram for a typical signalised T-junctionA variety of different control systems are used to operate signal cycles smoothly, ranging from simple clockwork mechanisms to sophisticated computerised control systems. Computerised systems are normally actuated, i.e. controlled by loop detectors or other sensors on junction approaches. Area-wide coordination can allow green wave systems to be set up for vehicles or cycle tracks.[61] Smart traffic light systems combine traditional actuation, a wider array of sensors and artificial intellegence to further improve performance of signal systems.[62] A traffic signal junction or crossing is typically controlled by a controller mounted inside a cabinet nearby.[63]
"Phases" (or "signal groups" in Australia and New Zealand) are indications show simultaneously, e.g. multiple green lights which control the same traffic approach. A "movement" is any path through the junction which vehicles or pedestrians are permitted to take, which is "conflicting" if these paths cross one another. A stage (or "phase" in ANZ) is a group of non-conflicting phases which move at the same time. The stages are collectively known as a "cycle".[64] The time between two conflicting green phases is called an "intergreen period", which is set at an appropriate length for the junction to safely clear, especially for turning traffic which may be waiting in the centre of the junction. This often results in an all red stage, when all approaches are shown a red light and no vehicle can proceed. This all red is sometimes extended to allow a pedestrian scramble, where pedestrians can cross the empty junction in any direction all at once.[65] Some signals have no "all red" phase: the light turns green for cross traffic the instant the other light turns red.[c]
Many traffic light installations are fitted with vehicle actuation, i.e. detection, to improve the flexibility of traffic systems to respond to varying traffic flows. Detectors come in the form of digital sensors fitted to the signal heads or induction loops within the road surface. Induction loops are beneficial due to their smaller chance of breakdown, but their simplicity can limit their ability to handle some situations, particularly involving lighter vehicles such as motorcycles or pedal cycles.[66] 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.[67]
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Traffic light with time in Tehran, IranThe timing of the intergreen is usually based on the size of the intersection, which can range from two to five seconds.[citation needed] Modelling programs include the ability to calculate intergreen times automatically. Intergreen periods are determined by calculating the path distance for every conflict point in the junction, which is the distance travelled to the conflict point by the movement losing right of way minus the distance travelled to the same conflict point by the movement gaining right of way using the possible conflict points (including with pedestrians) and calculating both the time it would take the last vehicle to clear the furthest collision point and the first vehicle from the next stage to arrive at the conflict point. At actuated junctions, integreens can be varied to account for traffic conditions.[19]
Engineers also need to set the amber timings (and red-amber, where appropriate), which is normally standardised by a traffic authority. For example, in the UK, the amber time is fixed nationally at three seconds and the red-amber time at two seconds, which results in a minimum intergreen time of five seconds (plus any all-red time).[19] The US also uses a minimum of three seconds, but local traffic authorities can make timings longer, especially on wider, suburban roads. This variation has resulted in controversy when municipalities with shorter amber times use red light cameras.[68] Where pedestrian signals are used, the timing of the "inivitation to cross" &#; the period where a steady walk signal shows &#; and clearance periods &#; time when the walk signal flashes or no signal is shown &#; need to be calculated. This is normally set against a design speed, e.g. 1.2 m/s (3.9 ft/s). Similarly, these can be made extendable using sensors, allowing slower-moving pedestrians more time to cross the street.[19]
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National or sub-national highway authorities often issue guidance documents on the specification of traffic signals and design of signalised intersections according to national or local regulations. For example, in the United States the Federal Highway Administration issues the Manual on Uniform Traffic Control Devices and the Signalized Intersections Information Guide, which is a synthesis of best practices and treatments to help practitioners make informed decisions.[69]
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An LED 50-watt typical lane control signal head Lane control signals installed on the Old Champlain Bridge in Montréal, CanadaVariable lane control is a form of intelligent transportation systems which involve the use of lane-use control signals, typically on a gantry above a carriageway. These lights are used in tidal flow systems to allow or forbid traffic to use one or more of the available lanes by the use of green lights or arrows (to permit) or by red lights or crosses (to prohibit).[70] 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.[70]
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.[citation needed]
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 500 ft (150 m) 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.[citation needed]
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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.
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California attempts to discourage red light running by posting the minimum fine.Traffic lights control flows of traffic using social norms and legal rules. In most jurisdictions, it is against the law to disobey traffic signals and the police, or devices such as red light cameras, can issue fines or other penalties &#; and in some cases prosecute &#; drivers who break those laws.[71] US-based studies have found that the majority of drivers think that it is dangerous to run a red light at speed and the most common reason for red light running include inattentive driving, following an oversized vehicle or during inclement weather.[72][73]
The rules governing traffic light junctions for vehicles differ by jurisdiction. For example, it is common in North America that drivers can turn kerb-to-kerb (i.e. turning right at most junctions), even when a red light shows.[74][75] On the other hand, this turn on red rule is uncommon in Europe, unless an arrow signal or traffic sign specifically permits it.[76][77][78][79]
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Conventional traffic signal lighting, still common in some areas, uses a standard light bulb. The light then bounces off a mirrored glass or polished aluminium reflector bowl, and out through a polycarbonate plastic or glass signal lens. In some signals, these lenses were cut to include a specific refracting pattern. Traditionally, incandescent and halogen bulbs were used. Because of the low efficiency of light output and a single point of failure (filament burnout), some traffic authorities are choosing to retrofit traffic signals with LED arrays that consume less power, have increased light output, and last significantly longer.[citation needed] 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.[80][81] As a response to the safety concerns, a heating element on the lens was developed.[82][83]
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top) and from the signal's intended viewing area (bottom).From off-axis, these signals appear to be "off" or invisible to adjacent lanes of traffic during the daytime. Only a faint glow can be seen when viewed at night.Traffic signals installed in Shelton, Washington , seen off-axis from the intended viewing area () and from the signal's intended viewing area ().From off-axis, these signals appear to be "off" or invisible to adjacent lanes of traffic during the daytime. Only a faint glow can be seen when viewed at night.
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.[citation needed]
Using a special aluminium foil-based adhesive tape, these signals are "masked" or programmed by the programming lens so that only certain lanes of traffic will view the indication. At the front of these programmable visibility signals is a 12" Fresnel lens, each lens tinted to meet United States Institute of Transportation Engineers (ITE) chromaticity and luminance standards. The Fresnel lens collimates the light output created by the lamp and creates a uniform display of light for the lane in which it is intended.
In addition to being positioned and mounted for desired visibility for their respective traffic, some traffic lights are also aimed, louvered, or shaded to minimize misinterpretation from other lanes. For example, a Fresnel lens on an adjacent through-lane signal may be aimed to prevent left-turning traffic from anticipating its own green arrow. Intelight Inc. manufactures a programmable traffic signal that uses a software-controlled LED array and electronics to steer the light beam toward the desired approach.[84] 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.
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In the United States, traffic lights are currently designed with lights approximately 12 inches (300 mm) in diameter. Previously the standard had been 8 inches (200 mm); 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 8 inches (200 mm) on the same light.
In the United Kingdom, 12-inch lights were implemented only with Mellor Design Signal heads designed by David Mellor. These were designed for symbolic optics to compensate for the light loss caused by the symbol. However, following a study sponsored by the UK Highways Agency and completed by Aston University, Birmingham, UK, an enhanced optical design was introduced in the mid-s. Criticism[by whom?] of sunlight washout (cannot see the illuminated signal due to sunlight falling on it), and sun-phantom (signal appearing to be illuminated even when not due to sunlight reflecting from the parabolic mirror at low sun angles), led to the design of a signal that used lenslets to focus light from a traditional incandescent bulb through apertures in a matt black front mask. This cured both problems in an easily manufactured solution. This design proved successful and was taken into production by a number of traffic signal manufacturers through the engineering designs of Dr. Mark Aston, working firstly at the SIRA Ltd in Kent, and latterly as an independent optical designer.[citation needed]
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 8 inches (200 mm) could be designed to give the same output as plain lenses, so a larger surface area was unnecessary. Consequently, lights of 12 inches (300 mm) are no longer approved for use in the UK and all lights installed on new installations have to be 200 mm (8 in) in accordance with TSRGD (Traffic Signs Regulations and General Directions). Exemptions are made for temporary or replacement signals.[citation needed]
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The MUTCD identifies five types of traffic light mounts. On pedestals, signal heads are mounted on a single pole (this is the normal installation method for the UK).[86][19] On mast arms, signal heads are mounted on a rigid arm over the road protuding from the pole. On strained poles, signals are suspended over a roadway on a wire, attached to poles at opposite kerbs. This is the most common installation method in the United States. Unipoles are similar to strain poles, but a single structure over the road, rather than two poles linked with wire. Finally, signals can be attached to existing structures such as an overpass.[86] 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.[87]
Signals can either be placed nearside &#; between the stop line and the kerbline of the intersecting road &#; or farside &#; on the opposite side of the junction. In European countries, signals are often placed on the nearside.[88] In the UK, at least two signal heads are required (known as the primary and secondary heads), one of which is normally nearside and the other of which could be nearside or farside.[19] In the US, signals are normally located farside, though in some states, nearside signals are also used. Nearside signals can be beneficial to road safety, as drivers have more time to see a red light and are less likely to encroach on pedestrian crossings.[88]
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Drivers spend on average around 2% of journey time passing through signalised junctions.[89] 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.[90] Hans Monderman, the innovative Dutch traffic engineer, and pioneer of shared space schemes, was sceptical of their role, and is quoted as having said of them: "We only want traffic lights where they are useful and I haven't found anywhere where they are useful yet."[91]
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.[89]
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%.[92] 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 and , the city of Philadelphia, Pennsylvania, removed signals at 199 intersections that were not warranted. On average, the intersections had 24% fewer crashes after the unwarranted signals were removed.[92] The traffic lights had been erected in the s because of since-resolved protests over traffic. By , over 800 traffic lights had been removed at 426 intersections, and the number of crashes at these intersections dropped by 60%.[93]
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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.
The International Municipal Signal Association provides input as to standards concerning traffic signals and control devices. One example is the input the association provided for the Manual on Uniform Traffic Control Devices (MUTCD).[94] The MUTCD is issued by the Federal Highway Administration (FHWA) of the United States Department of Transportation (USDOT).[95]
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:[96]
In the US, 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.
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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.[citation needed]
Traffic lights have also been used in computer software, such as the macOS user interface, and in pieces of artwork, particularly Traffic Light Tree in London, UK.
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Automobile racing circuits can also use standard traffic signals to indicate to racing car drivers the status of racing. On an oval track, four sets may be used, two facing a straight-away and two facing the middle of the 180-degree turn between straight-away. Green would indicate racing is underway, while amber would indicate to slow or while following a pace car; red would indicate to stop, probably for emergency reasons.
Scuderia Ferrari, a Formula One racing team, formerly used a traffic light system during their pit stops to signal to their drivers when to leave the pits.[citation needed] 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 Singapore Grand Prix, due to the fact that it heavily delayed Felipe Massa during the race, when he was in the lead. Usually, the system was automatic, but heavy traffic in the pit lane forced the team to operate it manually. A mechanic accidentally pressed the green light button when the fuel hose was still attached to the car, causing Massa to drive off, towing the fuel hose along. Additionally, Massa drove into the path of Adrian Sutil, earning him a penalty. He finally stopped at the end of the pit lane, forcing Ferrari's mechanics to sprint down the whole of the pit lane to remove the hose. As a result of this, and the penalty he also incurred, Massa finished 13th. Ferrari decided to use a traditional "lollipop" for the remainder of the 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. [citation needed]
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The colours red, amber, and green are often used as a simple-to-understand rating system for products and processes. It may be extended by analogy to provide a greater range of intermediate colours, with red and green at the extremes.[97]
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In Unicode, the symbol for U+1F6A5 &#; HORIZONTAL TRAFFIC LIGHT is HORIZONTAL TRAFFIC LIGHT and U+1F6A6 &#; VERTICAL TRAFFIC LIGHT is VERTICAL TRAFFIC LIGHT.
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clarification needed
]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 dependent on the conditions of the roadway (i.e. weather, falling rocks, risk of wildlife, etc.), such as in British Columbia, Canada.
The Barnes Dance 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.
citation needed
]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
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Support:
01 The features of traffic control signals of interest to road users are the location, design, and meaning of the signal indications. Uniformity in the design features that affect the traffic to be controlled, as set forth in this Manual, is especially important for the safety and efficiency of operations.
02 Traffic control signals can be operated in pretimed, semi-actuated, or full-actuated modes. For isolated (non-interconnected) signalized locations on rural high-speed highways, full-actuated mode with advance vehicle detection on the high-speed approaches is typically used. These features are designed to reduce the frequency with which the onset of the yellow change interval is displayed when high-speed approaching vehicles are in the "dilemma zone" such that the drivers of these high-speed vehicles find it difficult to decide whether to stop or proceed.
Standard:
03 When a traffic control signal is not in operation, such as before it is placed in service, during seasonal shutdowns, or when it is not desirable to operate the traffic control signal, the signal faces shall be covered, turned, or taken down to clearly indicate that the traffic control signal is not in operation.
Support:
04 Seasonal shutdown is a condition in which a permanent traffic signal is turned off or otherwise made non-operational during a particular season when its operation is not justified. This might be applied in a community where tourist traffic during most of the year justifies the permanent signalization, but a seasonal shutdown of the signal during an annual period of lower tourist traffic would reduce delays; or where a major traffic generator, such as a large factory, justifies the permanent signalization, but the large factory is shut down for an annual factory vacation for a few weeks in the summer.
Standard:
05 A traffic control signal shall control traffic only at the intersection or midblock location where the signal faces are placed.
06 Midblock crosswalks shall not be signalized if they are located within 300 feet from the nearest traffic control signal, unless the proposed traffic control signal will not restrict the progressive movement of traffic.
Guidance:
07 A midblock crosswalk location should not be controlled by a traffic control signal if the crosswalk is located within 100 feet from side streets or driveways that are controlled by STOP signs or YIELD signs.
08 Engineering judgment should be used to determine the proper phasing and timing for a traffic control signal. Since traffic flows and patterns change, phasing and timing should be reevaluated regularly and updated if needed.
09 Traffic control signals within 1/2 mile of one another along a major route or in a network of intersecting major routes should be coordinated, preferably with interconnected controller units. Where traffic control signals that are within 1/2 mile of one another along a major route have a jurisdictional boundary or a boundary between different signal systems between them, coordination across the boundary should be considered.
Support:
10 Signal coordination need not be maintained between control sections that operate on different cycle lengths.
11 For coordination with grade crossing signals and movable bridge signals, see Sections 4D.27, 4J.03, 8C.09, and 8C.10.
Guidance:
01 Prior to installing any traffic control signal, the responsibility for the maintenance of the signal and all of the appurtenances, hardware, software, and the timing plan(s) should be clearly established. The responsible agency should provide for the maintenance of the traffic control signal and all of its appurtenances in a competent manner.
02 To this end the agency should:
Support:
01 Chapter 4E contains additional information regarding pedestrian signals and Chapter 4F contains additional information regarding pedestrian hybrid beacons.
Standard:
02 The design and operation of traffic control signals shall take into consideration the needs of pedestrian as well as vehicular traffic.
03 If engineering judgment indicates the need for provisions for a given pedestrian movement, signal faces conveniently visible to pedestrians shall be provided by pedestrian signal heads (see Chapter 4E) or a vehicular signal face(s) for a concurrent vehicular movement.
Guidance:
04 Accessible pedestrian signals (see Sections 4E.09 through 4E.13) that provide information in non-visual formats (such as audible tones, speech messages, and/or vibrating surfaces) should be provided where determined appropriate by engineering judgment.
05 Where pedestrian movements regularly occur, pedestrians should be provided with sufficient time to cross the roadway by adjusting the traffic control signal operation and timing to provide sufficient crossing time every cycle or by providing pedestrian detectors.
06 If it is necessary or desirable to prohibit certain pedestrian movements at a traffic control signal location, No Pedestrian Crossing (R9-3) signs (see Section 2B.51) should be used if it is not practical to provide a barrier or other physical feature to physically prevent the pedestrian movements.
Support:
01 The "Uniform Vehicle Code" (see Section 1A.11) is the primary source for the standards for the meaning of vehicular signal indications to both vehicle operators and pedestrians as provided in this Section, and the standards for the meaning of separate pedestrian signal head indications as provided in Section 4E.02.
02 The physical area that is defined as being "within the intersection" is dependent upon the conditions that are described in the definition of intersection in Section 1A.13.
Standard:
03 The following meanings shall be given to highway traffic signal indications for vehicles and pedestrians:
Such vehicular traffic, including vehicles turning right or left or making a U-turn movement, shall yield the right-of-way to:
In addition, vehicular traffic turning left or making a U-turn movement to the left shall yield the right-of-way to other vehicles approaching from the opposite direction so closely as to constitute an immediate hazard during the time when such turning vehicle is moving across or within the intersection.
Such vehicular traffic, including vehicles turning right or left or making a U-turn movement, shall yield the right-of-way to:
Except when a traffic control device is in place prohibiting a turn on red or a steady RED ARROW signal indication is displayed, vehicular traffic facing a steady CIRCULAR RED signal indication is permitted to enter the intersection to turn right, or to turn left from a one-way street into a one-way street, after stopping. The right to proceed with the turn shall be subject to the rules applicable after making a stop at a STOP sign.
When a traffic control device is in place permitting a turn on a steady RED ARROW signal indication, vehicular traffic facing a steady RED ARROW signal indication is permitted to enter the intersection to make the movement indicated by the arrow signal indication, after stopping. The right to proceed with the turn shall be limited to the direction indicated by the arrow and shall be subject to the rules applicable after making a stop at a STOP sign.
Such vehicular traffic, including vehicles turning right or left or making a U-turn, shall yield the right-of-way to:
In addition, vehicular traffic turning left or making a U-turn to the left shall yield the right-of-way to other vehicles approaching from the opposite direction so closely as to constitute an immediate hazard during the time when such turning vehicle is moving across or within the intersection.
Such vehicular traffic, including vehicles turning right or left or making a U-turn, shall yield the right-of-way to:
In addition, vehicular traffic turning left or making a U-turn to the left shall yield the right-of-way to other vehicles approaching from the opposite direction so closely as to constitute an immediate hazard during the time when such turning vehicle is moving across or within the intersection.
Standard:
01 When a traffic control signal is being operated in a steady (stop-and-go) mode, at least one indication in each signal face shall be displayed at any given time.
02 A signal face(s) that controls a particular vehicular movement during any interval of a cycle shall control that same movement during all intervals of the cycle.
03 Steady signal indications shall be applied as follows:
Option:
04 If U-turns are permitted from the approach and a right-turn GREEN ARROW signal indication is simultaneously being displayed to road users making a right turn from the conflicting approach to the left, road users making a U-turn may be advised of the operation by the installation near the left-turn signal face of a U-TURN YIELD TO RIGHT TURN (R10-16) sign (see Section 2B.53).
05 If not otherwise prohibited, a steady straight-through green arrow signal indication may be used instead of a circular green signal indication in a signal face on an approach intersecting a one-way street to discourage wrong-way turns.
06 If not otherwise prohibited, steady red, yellow, and green turn arrow signal indications may be used instead of steady circular red, yellow, and green signal indications in a signal face on an approach where all traffic is required to turn or where the straight-through movement is not physically possible.
Link to FAMA
Support:
07 Section 4D.25 contains information regarding the signalization of approaches that have a shared left-turn/right-turn lane and no through movement.
Standard:
08 If supplemental signal faces are used, the following limitations shall apply:
09 A straight-through RED ARROW signal indication or a straight-through YELLOW ARROW signal indication shall not be displayed on any signal face, either alone or in combination with any other signal indication.
10 The following combinations of signal indications shall not be simultaneously displayed on any one signal face:
11 Additionally, the above combinations shall not be simultaneously displayed on an approach as a result of the combination of displays from multiple signal faces unless the display is created by a signal face(s) devoted exclusively to the control of a right-turning movement and:
12 The following combinations of signal indications shall not be simultaneously displayed on any one signal face or as a result of the combination of displays from multiple signal faces on an approach:
13 Except as otherwise provided in Sections 4F.03 and 4G.04, the same signal section shall not be used to display both a flashing yellow and a steady yellow indication during steady mode operation. Except as otherwise provided in Sections 4D.18, 4D.20, 4D.22, and 4D.24, the same signal section shall not be used to display both a flashing red and a steady red indication during steady mode operation.
Guidance:
14 No movement that creates an unexpected crossing of pathways of moving vehicles or pedestrians should be allowed during any green or yellow interval, except when all three of the following conditions are met:
Standard:
01 Each signal indication, except those used for pedestrian signal heads and lane-use control signals, shall be circular or arrow.
02 Letters or numbers (including those associated with countdown displays) shall not be displayed as part of a vehicular signal indication.
03 Strobes shall not be used within or adjacent to any signal indication.
04 Except for the flashing signal indications and the pre-emption confirmation lights that are expressly allowed by the provisions of this Chapter, flashing displays shall not be used within or adjacent to any signal indications.
05 Each circular signal indication shall emit a single color: red, yellow, or green.
06 Each arrow signal indication shall emit a single color: red, yellow, or green except that the alternate display (dual-arrow signal section) of a GREEN ARROW and a YELLOW ARROW signal indication, both pointing in the same direction, shall be permitted, provided that they are not displayed simultaneously.
07 The arrow, which shall show only one direction, shall be the only illuminated part of an arrow signal indication.
08 Arrows shall be pointed:
Figure 4D-1 Example of U-Turn Signal Face
09 Except as provided in Paragraph 10, the requirements of the publication entitled "Vehicle Traffic Control Signal Heads" (see Section 1A.11) that pertain to the aspects of the signal head design that affect the display of the signal indications shall be met.
Guidance:
10 The intensity and distribution of light from each illuminated signal lens should comply with the publications entitled "Vehicle Traffic Control Signal Heads" and "Traffic Signal Lamps" (see Section 1A.11).
Standard:
11 References to signal lenses in this section shall not be used to limit signal optical units to incandescent lamps within optical assemblies that include lenses.
Support:
12 Research has resulted in signal optical units that are not lenses, such as, but not limited to, light emitting diode (LED) traffic signal modules. Some units are practical for all signal indications, and some are practical for specific types such as visibility-limited signal indications.
Guidance:
13 If a signal indication is so bright that it causes excessive glare during nighttime conditions, some form of automatic dimming should be used to reduce the brilliance of the signal indication.
Standard:
01 There shall be two nominal diameter sizes for vehicular signal indications: 8 inches and 12 inches.
02 Except as provided in Paragraph 3 below, 12-inch signal indications shall be used for all signal sections in all new signal faces.
Option:
03 Eight-inch circular signal indications may be used in new signal faces only for:
04 Existing 8-inch circular signal indications that are not included in Items A through F in Paragraph 3 may be retained for the remainder of their useful service life.
Support:
01 Standardization of the number and arrangements of signal sections in vehicular traffic control signal faces enables road users who are color vision deficient to identify the illuminated color by its position relative to other signal sections.
Standard:
02 Unless otherwise provided in this Manual for a particular application, each signal face at a signalized location shall have three, four, or five signal sections. Unless otherwise provided in this Manual for a particular application, if a vertical signal face includes a cluster (see Section 4D.09), the signal face shall have at least three vertical positions.
03 A single-section signal face shall be permitted at a traffic control signal if it consists of a continuously-displayed GREEN ARROW signal indication that is being used to indicate a continuous movement.
04 The signal sections in a signal face shall be arranged in a vertical or horizontal straight line, except as otherwise provided in Section 4D.09.
05 The arrangement of adjacent signal sections in a signal face shall follow the relative positions listed in Sections 4D.09 or 4D.10, as applicable.
06 If a signal section that displays a CIRCULAR YELLOW signal indication is used, it shall be located between the signal section that displays the red signal indication and all other signal sections.
07 If a U-turn arrow signal section is used in a signal face for a U-turn to the left, its position in the signal face shall be the same as stated in Sections 4D.09 and 4D.10 for a left-turn arrow signal section of the same color. If a U-turn arrow signal section is used in a signal face for a U-turn to the right, its position in the signal face shall be the same as stated in Sections 4D.09 and 4D.10 for a right-turn arrow signal section of the same color.
08 A U-turn arrow signal indication pointing to the left shall not be used in a signal face that also contains a left-turn arrow signal indication. A U-turn arrow signal indication pointing to the right shall not be used in a signal face that also contains a right-turn arrow signal indication.
Option:
09 Within a signal face, two identical CIRCULAR RED or RED ARROW signal indications may be displayed immediately horizontally adjacent to each other in a vertical or horizontal signal face (see Figure 4D-2) for emphasis.
Figure 4D-2 Typical Arrangements of Signal Sections in Signal Faces That Do Not Control Turning Movements
10 Horizontally-arranged and vertically-arranged signal faces may be used on the same approach provided they are separated to meet the lateral separation spacing required in Section 4D.13.
Support:
11 Figure 4D-2 illustrates some of the typical arrangements of signal sections in signal faces that do not control separate turning movements. Figures 4D-6 through 4D-12 illustrate the typical arrangements of signal sections in left-turn signal faces. Figures 4D-13 through 4D-19 illustrate the typical arrangements of signal sections in right-turn signal faces.
Standard:
01 In each vertically-arranged signal face, all signal sections that display red signal indications shall be located above all signal sections that display yellow and green signal indications.
02 In vertically-arranged signal faces, each signal section that displays a YELLOW ARROW signal indication shall be located above the signal section that displays the GREEN ARROW signal indication to which it applies.
03 The relative positions of signal sections in a vertically-arranged signal face, from top to bottom, shall be as follows:
04 If a dual-arrow signal section (capable of alternating between the display of a GREEN ARROW and a YELLOW ARROW signal indication) is used in a vertically-arranged signal face, the dual-arrow signal section shall occupy the same position relative to the other sections as the signal section that displays the GREEN ARROW signal indication in a vertically-arranged signal face would occupy.
Option:
05 In a vertically-arranged signal face, signal sections that display signal indications of the same color may be arranged horizontally adjacent to each other at right angles to the basic straight line arrangement to form a clustered signal face (see Figures 4D-2, 4D-9, 4D-11, 4D-16, and 4D-18).
Standard:
06 Such clusters shall be limited to the following:
07 The signal section that displays a flashing yellow signal indication during steady mode operation:
Support:
08 Sections 4F.02 and 4G.04 contain exceptions to the provisions of this Section that are applicable to hybrid beacons.
Standard:
01 In each horizontally-arranged signal face, all signal sections that display red signal indications shall be located to the left of all signal sections that display yellow and green signal indications.
02 In horizontally-arranged signal faces, each signal section that displays a YELLOW ARROW signal indication shall be located to the left of the signal section that displays the GREEN ARROW signal indication to which it applies.
03 The relative positions of signal sections in a horizontally-arranged signal face, from left to right, shall be as follows:
04 If a dual-arrow signal section (capable of alternating between the display of a GREEN ARROW and a YELLOW ARROW signal indication) is used in a horizontally-arranged signal face, the signal section that displays the dual left-turn arrow signal indication shall be located immediately to the right of the signal section that displays the CIRCULAR YELLOW signal indication, the signal section that displays the straight-through GREEN ARROW signal indication shall be located immediately to the right of the signal section that displays the CIRCULAR GREEN signal indication, and the signal section that displays the dual right-turn arrow signal indication shall be located to the right of all other signal sections.
05 The signal section that displays a flashing yellow signal indication during steady mode operation:
Standard:
01 The signal faces for each approach to an intersection or a midblock location shall be provided as follows:
Option:
02 Where a movement (or a certain lane or lanes) at the intersection never conflicts with any other signalized vehicular or pedestrian movement, a continuously-displayed single-section GREEN ARROW signal indication may be used to inform road users that the movement is free-flow and does not need to stop.
Support:
03 In some circumstances where the through movement never conflicts with any other signalized vehicular or pedestrian movement at the intersection, such as at T-intersections with appropriate geometrics and/or pavement markings and signing, an engineering study might determine that the through movement (or certain lanes of the through movement) can be free-flow and not signalized.
Guidance:
04 If two or more left-turn lanes are provided for a separately controlled protected only mode left-turn movement, or if a left-turn movement represents the major movement from an approach, two or more primary left-turn signal faces should be provided.
05 If two or more right-turn lanes are provided for a separately controlled right-turn movement, or if a right-turn movement represents the major movement from an approach, two or more primary right-turn signal faces should be provided.
Support:
06 Locating primary signal faces overhead on the far side of the intersection has been shown to provide safer operation by reducing intersection entries late in the yellow interval and by reducing red signal violations, as compared to post-mounting signal faces at the roadside or locating signal faces overhead within the intersection on a diagonally-oriented mast arm or span wire. On approaches with two or more lanes for the through movement, one signal face per through lane, centered over each through lane, has also been shown to provide safer operation.
Guidance:
07 If the posted or statutory speed limit or the 85th-percentile speed on an approach to a signalized location is 45 mph or higher, signal faces should be provided as follows for all new or reconstructed signal installations (see Figure 4D-3):
Notes:
* A minimum of 2 through signal faces is always required (see Section 4D.11). These recommended numbers of through signal faces may be exceeded. Also, see cone of vision requirements otherwise indicated in Section 4D.13.
** If practical, all of the recommended number of primary through signal faces should be located overhead.
Figure 4D-3 Recommended Vehicular Signal Faces for Approaches with Posted, Statutory, or 85th Percentile Speed of 45 mph or Higher
08 This layout of signal faces should also be considered for any major urban or suburban arterial street with four or more lanes and for other approaches with speeds of less than 45 mph.
Standard:
01 The primary consideration in signal face placement, aiming, and adjustment shall be to optimize the visibility of signal indications to approaching traffic.
02 Road users approaching a signalized intersection or other signalized area, such as a midblock crosswalk, shall be given a clear and unmistakable indication of their right-of-way assignment.
03 The geometry of each intersection to be signalized, including vertical grades, horizontal curves, and obstructions as well as the lateral and vertical angles of sight toward a signal face, as determined by typical driver-eye position, shall be considered in determining the vertical, longitudinal, and lateral position of the signal face.
Guidance:
04 The two primary signal faces required as a minimum for each approach should be continuously visible to traffic approaching the traffic control signal, from a point at least the minimum sight distance provided in Table 4D-2 in advance of and measured to the stop line. This range of continuous visibility should be provided unless precluded by a physical obstruction or unless another signalized location is within this range.
Note: Distances in this table are derived from stopping sight distance plus an assumed queue length for shorter cycle lengths (60 to 75 seconds).
05 There should be legal authority to prohibit the display of any unauthorized sign, signal, marking, or device that interferes with the effectiveness of any official traffic control device (see Section 11-205 of the "Uniform Vehicle Code").
06 At signalized midblock crosswalks, at least one of the signal faces should be over the traveled way for each approach.
Standard:
07 If approaching traffic does not have a continuous view of at least two signal faces for at least the minimum sight distance shown in Table 4D-2, a sign (see Section 2C.36) shall be installed to warn approaching traffic of the traffic control signal.
Option:
08 If a sign is installed to warn approaching road users of the traffic control signal, the sign may be supplemented by a Warning Beacon (see Section 4L.03).
09 A Warning Beacon used in this manner may be interconnected with the traffic signal controller assembly in such a manner as to flash yellow during the period when road users passing this beacon at the legal speed for the roadway might encounter a red signal indication (or a queue resulting from the display of the red signal indication) upon arrival at the signalized location.
10 If the sight distance to the signal faces for an approach is limited by horizontal or vertical alignment, supplemental signal faces aimed at a point on the approach at which the signal indications first become visible may be used.
Guidance:
11 Supplemental signal faces should be used if engineering judgment has shown that they are needed to achieve intersection visibility both in advance and immediately before the signalized location.
12 If supplemental signal faces are used, they should be located to provide optimum visibility for the movement to be controlled.
Standard:
13 In cases where irregular street design necessitates placing signal faces for different street approaches with a comparatively small angle between their respective signal indications, each signal indication shall, to the extent practical, be visibility-limited by signal visors, signal louvers, or other means so that an approaching road user's view of the signal indication(s) controlling movements on other approaches is minimized.
14 Signal visors exceeding 12 inches in length shall not be used on free-swinging signal faces.
Guidance:
15 Signal visors should be used on signal faces to aid in directing the signal indication specifically to approaching traffic, as well as to reduce "sun phantom," which can result when external light enters the lens.
16 The use of signal visors, or the use of signal faces or devices that direct the light without a reduction in intensity, should be considered as an alternative to signal louvers because of the reduction in light output caused by signal louvers.
Option:
17 Special signal faces, such as visibility-limited signal faces, may be used such that the road user does not see signal indications intended for other approaches before seeing the signal indications for their own approach, if simultaneous viewing of both signal indications could cause the road user to be misdirected.
Guidance:
18 If the posted or statutory speed limit or the 85th-percentile speed on an approach to a signalized location is 45 mph or higher, signal backplates should be used on all of the signal faces that face the approach. Signal backplates should also be considered for use on signal faces on approaches with posted or statutory speed limits or 85th-percentile speeds of less than 45 mph where sun glare, bright sky, and/or complex or confusing backgrounds indicate a need for enhanced signal face target value.
Support:
19 The use of backplates enhances the contrast between the traffic signal indications and their surroundings for both day and night conditions, which is also helpful to older drivers.
Standard:
20 The inside of signal visors (hoods), the entire surface of louvers and fins, and the front surface of backplates shall have a dull black finish to minimize light reflection and to increase contrast between the signal indication and its background.
Option:
21 A yellow retroreflective strip with a minimum width of 1 inch and a maximum width of 3 inches may be placed along the perimeter of the face of a signal backplate to project a rectangular appearance at night.
Standard:
01 At least one and preferably both of the minimum of two primary signal faces required for the through movement (or the major turning movement if there is no through movement) on the approach shall be located between two lines intersecting with the center of the approach at a point 10 feet behind the stop line, one making an angle of approximately 20 degrees to the right of the center of the approach extended, and the other making an angle of approximately 20 degrees to the left of the center of the approach extended. The signal face that satisfies this requirement shall simultaneously satisfy the longitudinal placement requirement described in Section 4D.14 (see Figure 4D-4).
Figure 4D-4 Lateral and Longitudinal Location of Primary Signal Faces
02 If both of the minimum of two primary signal faces required for the through movement (or the major turning movement if there is no through movement) on the approach are post-mounted, they shall both be on the far side of the intersection, one on the right and one on the left of the approach lane(s).
03 The required signal faces for through traffic on an approach shall be located not less than 8 feet apart measured horizontally perpendicular to the approach between the centers of the signal faces.
04 If more than one separate turn signal face is provided for a turning movement and if one or both of the separate turn signal faces are located over the roadway, the signal faces shall be located not less than 8 feet apart measured horizontally perpendicular to the approach between the centers of the signal faces.
Guidance:
05 If a signal face controls a specific lane or lanes of an approach, its position should make it readily visible to road users making that movement.
Support:
06 Section 4D.11 contains additional provisions regarding lateral positioning of signal faces for approaches having a posted or statutory speed limit or an 85th-percentile speed of 45 mph or higher.
Standard:
07 If an exclusive left-turn, right-turn, or U-turn lane is present on an approach and if a primary separate turn signal face controlling that lane is mounted over the roadway, the primary separate turn signal face shall not be positioned any further to the right than the extension of the right-hand edge of the exclusive turn lane or any further to the left than the extension of the left-hand edge of the exclusive turn lane.
08 Supplemental turn signal faces mounted over the roadway shall not be subject to the positioning requirements in the previous paragraph.
Guidance:
09 For new or reconstructed signal installations, on an approach with an exclusive turn lane(s) for a left-turn (or U-turn to the left) movement and with opposing vehicular traffic, signal faces that display a CIRCULAR GREEN signal indication should not be post-mounted on the far-side median or mounted overhead above the exclusive turn lane(s) or the extension of the lane(s).
Standard:
10 If supplemental post-mounted signal faces are used, the following limitations shall apply:
Standard:
01 Except where the width of an intersecting roadway or other conditions make it physically impractical, the signal faces for each approach to an intersection or a midblock location shall be provided as follows:
The primary signal face that satisfies this requirement shall simultaneously satisfy the lateral placement requirement described in Section 4D.13 (see Figure 4D-4).
Support:
02 Section 4D.11 contains additional provisions regarding longitudinal positioning of signal faces for approaches having a posted or 85th-percentile speed of 45 mph or higher.
Guidance:
03 Supplemental near-side signal faces should be located as near as practical to the stop line.
Standard:
01 The top of the signal housing of a vehicular signal face located over any portion of a highway that can be used by motor vehicles shall not be more than 25.6 feet above the pavement.
02 For viewing distances between 40 and 53 feet from the stop line, the maximum mounting height to the top of the signal housing shall be as shown in Figure 4D-5.
Figure 4D-5 Maximum Mounting Height of Signal Faces Located Between 40 Feet and 53 Feet from Stop Line
03 The bottom of the signal housing and any related attachments to a vehicular signal face located over any portion of a highway that can be used by motor vehicles shall be at least 15 feet above the pavement.
04 The bottom of the signal housing (including brackets) of a vehicular signal face that is vertically arranged and not located over a roadway:
05 The bottom of the signal housing (including brackets) of a vehicular signal face that is horizontally arranged and not located over a roadway:
Standard:
01 Signal faces mounted at the side of a roadway with curbs at less than 15 feet from the bottom of the housing and any related attachments shall have a horizontal offset of not less than 2 feet from the face of a vertical curb, or if there is no curb, not less than 2 feet from the edge of a shoulder.
Standard:
01 In Sections 4D.17 through 4D.20, provisions applicable to left-turn movements and left-turn lanes shall also apply to signal indications for U-turns to the left that are provided at locations where left turns are prohibited or not geometrically possible.
Support:
02 Left-turning traffic is controlled by one of four modes as follows:
Option:
03 In areas having a high percentage of older drivers, special consideration may be given to the use of protected only mode left-turn phasing, when appropriate.
Standard:
04 During a permissive left-turn movement, the signal faces for through traffic on the opposing approach shall simultaneously display green or steady yellow signal indications. If pedestrians crossing the lane or lanes used by the permissive left-turn movement to depart the intersection are controlled by pedestrian signal heads, the signal indications displayed by those pedestrian signal heads shall not be limited to any particular display during the permissive left-turn movement.
05 During a protected left-turn movement, the signal faces for through traffic on the opposing approach shall simultaneously display steady CIRCULAR RED signal indications. If pedestrians crossing the lane or lanes used by the protected left-turn movement to depart the intersection are controlled by pedestrian signal heads, the pedestrian signal heads shall display a steady UPRAISED HAND (symbolizing DONT WALK) signal indication during the protected left-turn movement.
06 A protected only mode left-turn movement that does not begin and terminate at the same time as the adjacent through movement shall not be provided on an approach unless an exclusive left-turn lane exists.
07 A yellow change interval for the left-turn movement shall not be displayed when the status of the left-turn operation is changing from permissive to protected within any given signal sequence.
08 If the operating mode changes among the protected only mode and/or the protected/permissive mode and/or the permissive only mode during different periods of the day or as traffic conditions change, the requirements in Sections 4D.18 through 4D.20 that are appropriate to that mode of operation shall be met, subject to the following:
Option:
09 Additional static signs or changeable message signs may be used to meet the requirements for the variable left-turn mode or to inform drivers that left-turn green arrows will not be available during certain times of the day.
Support:
10 Sections 4D.17 through 4D.20 describe the use of the following two types of signal faces for controlling left-turn movements:
11 Section 4D.13 contains provisions regarding the lateral positioning of signal faces that control left-turn movements.
12 It is not necessary that the same mode of left-turn operation or same type of left-turn signal face be used on every approach to a signalized location. Selecting different modes and types of left-turn signal faces for the various approaches to the same signalized location is acceptable.
Option:
13 A signal face that is shared by left-turning and right-turning traffic may be provided for a shared left-turn/right-turn lane on an approach that has no through traffic (see Section 4D.25).
Standard:
01 If a shared signal face is provided for a permissive only mode left turn, it shall meet the following requirements (see Figure 4D-6):
Figure 4D-6 Typical Position and Arrangements of Shared Signal Faces for Permissive Only Mode Left Turns
02 If a separate left-turn signal face is being operated in a permissive only left-turns mode, a CIRCULAR GREEN signal indication shall not be used in that face.
03 If a separate left-turn signal face is being operated in a permissive only left-turn mode and a flashing left-turn YELLOW ARROW signal indication is provided, it shall meet the following requirements (see Figure 4D-7):
Figure 4D-7 Typical Position and Arrangements of Separate Signal Faces with Flashing Yellow Arrow for Permissive Only Mode Left Turns
Option:
04 A separate left-turn signal face with a flashing left-turn RED ARROW signal indication during the permissive left-turn movement may be used for unusual geometric conditions, such as wide medians with offset left-turn lanes, but only when an engineering study determines that each and every vehicle must successively come to a full stop before making a permissive left turn.
Standard:
05 If a separate left-turn signal face is being operated in a permissive only left-turn mode and a flashing left-turn RED ARROW signal indication is provided, it shall meet the following requirements (see Figure 4D-8):
Figure 4D-8 Typical Position and Arrangements of Separate Signal Faces with Flashing Red Arrow for Permissive Only Mode and Protected/Permissive Mode Left Turns
Option:
06 The requirements of Item A in Paragraph 5 may be met by a vertically-arranged signal face with a horizontal cluster of two left-turn RED ARROW signal indications, the left-most of which displays a steady indication and the right-most of which displays a flashing indication (see Figure 4D-8).
Standard:
01 A shared signal face shall not be used for protected only mode left turns unless the CIRCULAR GREEN and left-turn GREEN ARROW signal indications always begin and terminate together. If a shared signal face is provided for a protected only mode left turn, it shall meet the following requirements (see Figure 4D-9):
Figure 4D-9 Typical Positions and Arrangements of Shared Signal Faces for Protected Only Mode Left Turns
Option:
02 A straight-through GREEN ARROW signal indication may be used instead of the CIRCULAR GREEN signal indication in Items A and B in Paragraph 1 on an approach where right turns are prohibited and a straight-through GREEN ARROW signal indication is also used instead of a CIRCULAR GREEN signal indication in the other signal face(s) for through traffic.
Standard:
03 If a separate left-turn signal face is provided for a protected only mode left turn, it shall meet the following requirements (see Figure 4D-10):
Figure 4D-10 Typical Position and Arrangements of Separate Signal Faces for Protected Only Mode Left Turns
Standard:
01 If a shared signal face is provided for a protected/permissive mode left turn, it shall meet the following requirements (see Figure 4D-11):
Figure 4D-11 Typical Position and Arrangements of Shared Signal Faces for Protected/Permissive Mode Left Turns
02 If a separate left-turn signal face is being operated in a protected/permissive left-turn mode, a CIRCULAR GREEN signal indication shall not be used in that face.
03 If a separate left-turn signal face is being operated in a protected/permissive left-turn mode and a flashing left-turn yellow arrow signal indication is provided, it shall meet the following requirements (see Figure 4D-12):
Figure 4D-12 Typical Position and Arrangements of Separate Signal Faces with Flashing Yellow for Protected/Permissive Mode and Protected Only Mode Left Turns
Option:
04 A separate left-turn signal face with a flashing left-turn RED ARROW signal indication during the permissive left-turn movement may be used for unusual geometric conditions, such as wide medians with offset left-turn lanes, but only when an engineering study determines that each and every vehicle must successively come to a full stop before making a permissive left turn.
Standard:
05 If a separate left-turn signal face is being operated in a protected/permissive left-turn mode and a flashing left-turn RED arrow signal indication is provided, it shall meet the following requirements (see Figure 4D-8):
Option:
06 The requirements of Item A in Paragraph 5 may be met by a vertically-arranged signal face with a horizontal cluster of two left-turn RED ARROW signal indications, the left-most of which displays a steady indication and the right-most of which displays a flashing indication (see Figure 4D-8).
Standard:
01 In Sections 4D.21 through 4D.24, provisions applicable to right-turn movements and right-turn lanes shall also apply to signal indications for U-turns to the right that are provided at locations where right turns are prohibited or not geometrically possible.
Support:
02 Right-turning traffic is controlled by one of four modes as follows:
Standard:
03 During a permissive right-turn movement, the signal faces, if any, that exclusively control U-turn traffic that conflicts with the permissive right-turn movement (see Item F.1 in Section 4D.05) shall simultaneously display steady U-turn RED ARROW signal indications. If pedestrians crossing the lane or lanes used by the permissive right-turn movement to depart the intersection are controlled by pedestrian signal heads, the signal indications displayed by those pedestrian signal heads shall not be limited to any particular display during the permissive right-turn movement.
04 During a protected right-turn movement, the signal faces for left-turn traffic, if any, on the opposing approach shall not simultaneously display a steady left-turn GREEN ARROW or steady left-turn YELLOW ARROW signal indication, and signal faces, if any, that exclusively control U-turn traffic that conflicts with the protected right-turn movement (see Item F.1 in Section 4D.05) shall simultaneously display steady U-turn RED ARROW signal indications. If pedestrians crossing the lane or lanes used by the protected right-turn movement to depart the intersection are controlled by pedestrian signal heads, the pedestrian signal heads shall display a steady UPRAISED HAND (symbolizing DONT WALK) signal indication during the protected right-turn movement.
05 A protected only mode right-turn movement that does not begin and terminate at the same time as the adjacent through movement shall not be provided on an approach unless an exclusive right-turn lane exists.
06 A yellow change interval for the right-turn movement shall not be displayed when the status of the right-turn operation is changing from permissive to protected within any given signal sequence.
07 If the operating mode changes among the protected only mode and/or the protected/permissive mode and/or the permissive only mode during different periods of the day or as traffic conditions change, the requirements in Sections 4D.22 through 4D.24 that are appropriate to that mode of operation shall be met, subject to the following:
Option:
08 Additional static signs or changeable message signs may be used to meet the requirements for the variable right-turn mode or to inform drivers that right-turn green arrows will not be available during certain times of the day.
Support:
09 Sections 4D.21 through 4D.24 describe the use of the following two types of signal faces for controlling right-turn movements:
10 Section 4D.13 contains provisions regarding the lateral positioning of signal faces that control right-turn movements.
11 It is not necessary that the same mode of right-turn operation or same type of right-turn signal face be used on every approach to a signalized location. Selecting different modes and types of right-turn signal faces for the various approaches to the same signalized location is acceptable.
Option:
12 A signal face that is shared by left-turning and right-turning traffic may be provided for a shared left-turn/right-turn lane on an approach that has no through traffic (see Section 4D.25).
Standard:
01 If a shared signal face is provided for a permissive only mode right turn, it shall meet the following requirements (see Figure 4D-13):
Figure 4D-13 Typical Positions and Arrangements of Shared Signal Faces for Permissive Only Mode Right Turns
02 If a separate right-turn signal face is being operated in a permissive only right-turn mode, a CIRCULAR GREEN signal indication shall not be used in that face.
03 If a separate right-turn signal face is being operated in a permissive only right-turn mode and a flashing right-turn yellow arrow signal indication is provided, it shall meet the following requirements (see Figure 4D-14):
Figure 4D-14 Typical Position and Arrangements of Separate Signal Faces with Flashing Yellow Arrow for Permissive Only Mode Right Turns
Option:
04 When an engineering study determines that each and every vehicle must successively come to a full stop before making a permissive right turn, a separate right-turn signal face with a flashing right-turn RED ARROW signal indication during the permissive right-turn movement may be used.
Standard:
05 If a separate right-turn signal face is being operated in a permissive only right-turn mode and a flashing right-turn RED arrow signal indication is provided, it shall meet the following requirements (see Figure 4D-15):
Figure 4D-15 Typical Position and Arrangements of Separate Signal Faces with Flashing Red Arrow for Permissive Only Mode and Protected/Permissive Mode Right Turns
Option:
06 The requirements of Item A.1 in Paragraph 5 may be met by a vertically-arranged signal face with a horizontal cluster of two right-turn RED ARROW signal indications, the left-most of which displays a steady indication and the right-most of which displays a flashing indication (see Figure 4D-15).
Standard:
01 A shared signal face shall not be used for protected only mode right turns unless the CIRCULAR GREEN and right-turn GREEN ARROW signal indications always begin and terminate together. If a shared signal face is provided for a protected only right turn, it shall meet the following requirements (see Figure 4D-16):
Figure 4D-16 Typical Positions and Arrangements of Shared Signal Faces for Protected Only Mode Right Turns
Option:
02 A straight-through GREEN ARROW signal indication may be used instead of the CIRCULAR GREEN signal indication in Items A and B in Paragraph 1 on an approach where left turns are prohibited and a straight-through GREEN ARROW signal indication is also used instead of a CIRCULAR GREEN signal indication in the other signal face(s) for through traffic.
Standard:
03 If a separate right-turn signal face is provided for a protected only mode right turn, it shall meet the following requirements (see Figure 4D-17):
Figure 4D-17 Typical Position and Arrangements of Separate Signal Faces for Protected Only Mode Right Turns
Standard:
01 If a shared signal face is provided for a protected/permissive mode right turn, it shall meet the following requirements (see Figure 4D-18):
Figure 4D-18 Typical Positions and Arrangements of Shared Signal Faces for Protected/Permissive Mode Right Turns
02 If a separate right-turn signal face is being operated in a protected/permissive right-turn mode, a CIRCULAR GREEN signal indication shall not be used in that face.
03 If a separate right-turn signal face is being operated in a protected/permissive right-turn mode and a flashing right-turn yellow arrow signal indication is provided, it shall meet the following requirements (see Figure 4D-19):
Figure 4D-19 Typical Position and Arrangements of Separate Signal Faces with Flashing Yellow Arrow for Protected/Permissive Mode and Protected Only Mode Right Turns
Option:
04 When an engineering study determines that each and every vehicle must successively come to a full stop before making a permissive right turn, a separate signal face that has a flashing right-turn RED ARROW signal indication during the permissive right-turn movement may be used.
Standard:
05 If a separate right-turn signal face is being operated in a protected/permissive right-turn mode and a flashing right-turn RED arrow signal indication is provided, it shall meet the following requirements (see Figure 4D-15):
Option:
06 The requirements of Item A.1 in Paragraph 5 may be met by a vertically-arranged signal face with a horizontal cluster of two right-turn RED ARROW signal indications, the left-most of which displays a steady indication and the right-most of which displays a flashing indication (see Figure 4D-15).
Support:
01 A lane that is shared by left-turn and right-turn movements is sometimes provided on an approach that has no through movement, such as the stem of a T-intersection or where the opposite approach is a one-way roadway in the opposing direction.
Standard:
02 When a shared left-turn/right-turn lane exists on a signalized approach, the left-turn and right-turn movements shall start and terminate simultaneously and the red signal indication used in each of the signal faces on the approach shall be a CIRCULAR RED.
Support:
03 This requirement for the use of CIRCULAR RED signal indications in signal faces for approaches having a shared lane for left-turn and right-turn movements is a specific exception to other provisions in this Chapter that would otherwise require the use of RED ARROW signal indications.
Standard:
04 The signal faces provided for an approach with a shared left-turn/right-turn lane and no through movement shall be one of the following:
Support:
05 Figure 4D-20 illustrates application of these Standards on approaches that have only a shared left-turn/right-turn lane, and on approaches that have one or more exclusive turn lanes in addition to the shared left-turn/right-turn lane.
Figure 4D-20, Sheet 1 Signal Indications for Approaches with a Shared Left-Turn/Right-Turn Lane and No Through Movement (Sheet 1 of 3)
Option:
06 If the lane-use regulations on an approach are variable such that at certain times all of the lanes on the approach are designated as exclusive turn lanes and no lane is designated as a shared left-turn/right-turn lane:
Standard:
01 A steady yellow signal indication shall be displayed following every CIRCULAR GREEN or GREEN ARROW signal indication and following every flashing YELLOW ARROW or flashing RED ARROW signal indication displayed as a part of a steady mode operation. This requirement shall not apply when a CIRCULAR GREEN, a flashing YELLOW ARROW, or a flashing RED ARROW signal indication is followed immediately by a GREEN ARROW signal indication.
02 The exclusive function of the yellow change interval shall be to warn traffic of an impending change in the right-of-way assignment.
03 The duration of the yellow change interval shall be determined using engineering practices.
Support:
04 Section 4D.05 contains provisions regarding the display of steady CIRCULAR YELLOW signal indications to approaches from which drivers are allowed to make permissive left turns.
Guidance:
05 When indicated by the application of engineering practices, the yellow change interval should be followed by a red clearance interval to provide additional time before conflicting traffic movements, including pedestrians, are released.
Standard:
06 When used, the duration of the red clearance interval shall be determined using engineering practices.
Support:
07 Engineering practices for determining the duration of yellow change and red clearance intervals can be found in ITE's "Traffic Control Devices Handbook" and in ITE's "Manual of Traffic Signal Design" (see Section 1A.11).
Standard:
08 The durations of yellow change intervals and red clearance intervals shall be consistent with the determined values within the technical capabilities of the controller unit.
09 The duration of a yellow change interval shall not vary on a cycle-by-cycle basis within the same signal timing plan.
10 Except as provided in Paragraph 12, the duration of a red clearance interval shall not be decreased or omitted on a cycle-by-cycle basis within the same signal timing plan.
Option:
11 The duration of a red clearance interval may be extended from its predetermined value for a given cycle based upon the detection of a vehicle that is predicted to violate the red signal indication.
12 When an actuated signal sequence includes a signal phase for permissive/protected (lagging) left-turn movements in both directions, the red clearance interval may be shown during those cycles when the lagging left-turn signal phase is skipped and may be omitted during those cycles when the lagging left-turn signal phase is shown.
13 The duration of a yellow change interval or a red clearance interval may be different in different signal timing plans for the same controller unit.
Guidance:
14 A yellow change interval should have a minimum duration of 3 seconds and a maximum duration of 6 seconds. The longer intervals should be reserved for use on approaches with higher speeds.
15 Except when clearing a one-lane, two-way facility (see Section 4H.02) or when clearing an exceptionally wide intersection, a red clearance interval should have a duration not exceeding 6 seconds.
Standard:
16 Except for warning beacons mounted on advance warning signs on the approach to a signalized location (see Section 2C.36), signal displays that are intended to provide a "pre-yellow warning" interval, such as flashing green signal indications, vehicular countdown displays, or other similar displays, shall not be used at a signalized location.
Support:
17 The use of signal displays (other than warning beacons mounted on advance warning signs) that convey a "pre-yellow warning" have been found by research to increase the frequency of crashes.
Option:
01 Traffic control signals may be designed and operated to respond to certain classes of approaching vehicles by altering the normal signal timing and phasing plan(s) during the approach and passage of those vehicles. The alternative plan(s) may be as simple as extending a currently displayed green interval or as complex as replacing the entire set of signal phases and timing.
Support:
02 Preemption control (see definition in Section 1A.13) is typically given to trains, boats, emergency vehicles, and light rail transit.
03 Examples of preemption control include the following:
04 Priority control (see definition in Section 1A.13) is typically given to certain non-emergency vehicles such as light-rail transit vehicles operating in a mixed-use alignment and buses.
05 Examples of priority control include the following:
06 Some types or classes of vehicles supersede others when a traffic control signal responds to more than one type or class. In general, a vehicle that is more difficult to control supersedes a vehicle that is easier to control.
Option:
07 Preemption or priority control of traffic control signals may also be a means of assigning priority right-of-way to specified classes of vehicles at certain non-intersection locations such as on approaches to one-lane bridges and tunnels, movable bridges, highway maintenance and construction activities, metered freeway entrance ramps, and transit operations.
Standard:
08 During the transition into preemption control:
09 During preemption control and during the transition out of preemption control:
10 During priority control and during the transition into or out of priority control:
Guidance:
11 Except for traffic control signals interconnected with light rail transit systems, traffic control signals with railroad preemption or coordinated with flashing-light signal systems should be provided with a back-up power supply.
12 When a traffic control signal that is returning to a steady mode from a dark mode (typically upon restoration from a power failure) receives a preemption or priority request, care should be exercised to minimize the possibility of vehicles or pedestrians being misdirected into a conflict with the vehicle making the request.
Option:
13 During the change from a dark mode to a steady mode under a preemption or priority request, the display of signal indications that could misdirect road users may be prevented by one or more of the following methods:
Guidance:
14 If a traffic control signal is installed near or within a grade crossing or if a grade crossing with active traffic control devices is within or near a signalized highway intersection, Chapter 8C should be consulted.
15 Traffic control signals operating under preemption control or under priority control should be operated in a manner designed to keep traffic moving.
16 Traffic control signals that are designed to respond under preemption or priority control to more than one type or class of vehicle should be designed to respond in the relative order of importance or difficulty in stopping the type or class of vehicle. The order of priority should be: train, boat, heavy vehicle (fire vehicle, emergency medical service), light vehicle (law enforcement), light rail transit, rubber-tired transit.
Option:
17 A distinctive indication may be provided at the intersection to show that an emergency vehicle has been given control of the traffic control signal (see Section 11-106 of the "Uniform Vehicle Code"). In order to assist in the understanding of the control of the traffic signal, a common distinctive indication may be used where drivers from different agencies travel through the same intersection when responding to emergencies.
18 If engineering judgment indicates that light rail transit signal indications would reduce road user confusion that might otherwise occur if standard traffic signal indications were used to control these movements, light rail transit signal indications complying with Section 8C.11 and as illustrated in Figure 8C-3 may be used for preemption or priority control of the following exclusive movements at signalized intersections:
Standard:
01 The light source of a flashing signal indication shall be flashed continuously at a rate of not less than 50 or more than 60 times per minute.
02 The displayed period of each flash shall be a minimum of 1/2 and a maximum of 2/3 of the total flash cycle.
03 Flashing signal indications shall comply with the requirements of other Sections of this Manual regarding visibility-limiting or positioning of conflicting signal indications, except that flashing yellow signal indications for through traffic shall not be required to be visibility-limited or positioned to minimize visual conflict for road users in separately controlled turn lanes.
04 Each traffic control signal shall be provided with an independent flasher mechanism that operates in compliance with this Section.
05 The flashing operation shall not be terminated by removal or turn off of the controller unit or of the conflict monitor (malfunction management unit) or both.
06 A manual switch, a conflict monitor (malfunction management unit) circuit, and, if appropriate, automatic means shall be provided to initiate the flashing mode.
Option:
07 Based on engineering study or engineering judgment, traffic control signals may be operated in the flashing mode on a scheduled basis during one or more periods of the day rather than operated continuously in the steady (stop-and-go) mode.
Support:
08 Sections 4E.06 and 4E.09 contain information regarding the operation of pedestrian signal heads and accessible pedestrian signal detector pushbutton locator tones, respectively, during flashing operation.
Standard:
01 The transition from steady (stop-and-go) mode to flashing mode, if initiated by a conflict monitor (malfunction management unit) or by a manual switch, shall be permitted to be made at any time.
02 Programmed changes from steady (stop-and-go) mode to flashing mode shall be made under either of the following circumstances:
03 During programmed changes into flashing mode, no green signal indication or flashing yellow signal indication shall be terminated and immediately followed by a steady red or flashing red signal indication without first displaying the steady yellow signal indication.
Guidance:
01 When a traffic control signal is operated in the flashing mode, a flashing yellow signal indication should be used for the major street and a flashing red signal indication should be used for the other approaches unless flashing red signal indications are used on all approaches.
Standard:
02 When a traffic control signal is operated in the flashing mode, all of the green signal indications at the signalized location shall be dark (non-illuminated) and shall not be displayed in either a steady or flashing manner, except for single-section GREEN ARROW signal indications as provided elsewhere in this Section.
03 Flashing yellow signal indications shall be used on more than one approach to a signalized location only if those approaches do not conflict with each other.
04 Except as provided in Paragraph 5, when a traffic control signal is operated in the flashing mode, one and only one signal indication in every signal face at the signalized location shall be flashed.
Option:
05 If a signal face has two identical CIRCULAR RED or RED ARROW signal indications (see Section 4D.08), both of those identical signal indications may be flashed simultaneously.
Standard:
06 No steady indications, other than a single-section signal face consisting of a continuously-displayed GREEN ARROW signal indication that is used alone to indicate a continuous movement in the steady (stop-and-go) mode, shall be displayed at the signalized location during the flashing mode. A single-section GREEN ARROW signal indication shall remain continuously-displayed when the traffic control signal is operated in the flashing mode.
07 If a signal face includes both circular and arrow signal indications of the color that is to be flashed, only the circular signal indication shall be flashed.
08 All signal faces that are flashed on an approach shall flash the same color, either yellow or red, except that separate turn signal faces (see Sections 4D.17 and 4D.21) shall be permitted to flash a RED ARROW signal indication when the adjacent through movement signal indications are flashed yellow. Shared signal faces (see Sections 4D.17 and 4D.21) for turn movements shall not be permitted to flash a CIRCULAR RED signal indication when the adjacent through movement signal indications are flashed yellow.
09 The appropriate RED ARROW or YELLOW ARROW signal indication shall be flashed when a signal face consists entirely of arrow indications. A signal face that consists entirely of arrow indications and that provides a protected only turn movement during the steady (stop-and-go) mode or that provides a flashing yellow arrow or flashing red arrow signal indication for a permissive turn movement during the steady (stop-and-go) mode shall be permitted to flash the YELLOW ARROW signal indication during the flashing mode if the adjacent through movement signal indications are flashed yellow and if it is intended that a permissive turn movement not requiring a full stop by each turning vehicle be provided during the flashing mode.
Standard:
01 All changes from flashing mode to steady (stop-and-go) mode shall be made under one of the following procedures:
Guidance:
02 The steady red clearance interval provided during the change from red-red flashing mode to steady (stop-and-go) mode should have a duration of 6 seconds.
03 When changing from the yellow-red flashing mode to steady (stop-and-go) mode, if there is no common major-street green interval, the provision of a steady red clearance interval for the other approaches before changing from a flashing yellow or a flashing red signal indication to a green signal indication on the major approach should be considered.
Standard:
04 During programmed changes out of flashing mode, no flashing yellow signal indication shall be terminated and immediately followed by a steady red or flashing red signal indication without first displaying the steady yellow signal indication.
Option:
05 Because special midblock signals that rest in flashing circular yellow in the position normally occupied by the green signal indication do not have a green signal indication in the signal face, these signals may go directly from flashing circular yellow (in the position normally occupied by the green signal indication) to steady yellow without going first to a green signal indication.
Support:
01 A temporary traffic control signal is generally installed using methods that minimize the costs of installation, relocation, and/or removal. Typical temporary traffic control signals are for specific purposes, such as for one-lane, two-way facilities in temporary traffic control zones (see Chapter 4H), for a haul-road intersection, or for access to a site that will have a permanent access point developed at another location in the near future.
Standard:
02 Advance signing shall be used when employing a temporary traffic control signal.
03 A temporary traffic control signal shall:
Guidance:
04 A temporary traffic control signal should be used only if engineering judgment indicates that installing the signal will improve the overall safety and/or operation of the location.
05 The use of temporary traffic control signals by a work crew on a regular basis in their work area should be subject to the approval of the jurisdiction having authority over the roadway.
06 A temporary traffic control signal should not operate longer than 30 days unless associated with a longer-term temporary traffic control zone project.
07 For use of temporary traffic control signals in temporary traffic control zones, reference should be made to Section 6F.84.
Guidance:
01 The following items should be considered when placing signal supports and cabinets:
Support:
01 Traffic signal signs are sometimes used at highway traffic signal locations to instruct or guide pedestrians, bicyclists, or motorists. Among the signs typically used at or on the approaches to signalized locations are movement prohibition signs (see Section 2B.18), lane control signs (see Sections 2B.19 to 2B.22), pedestrian crossing signs (see Section 2B.51), pedestrian actuation signs (see Section 2B.52), traffic signal signs (see Sections 2B.53 and 2C.48), Signal Ahead warning signs (see Section 2C.36), Street Name signs (see Section 2D.43), and Advance Street Name signs (see Section 2D.44).
Guidance:
02 Regulatory, warning, and guide signs should be used at traffic control signal locations as provided in Part 2 and as specifically provided elsewhere in Part 4.
03 Traffic signal signs should be located adjacent to the signal face to which they apply.
Support:
04 Section 2B.19 contains information regarding the use of overhead lane control signs on signalized approaches where lane drops, multiple-lane turns involving shared through-and-turn lanes, or other lane-use regulations that would be unexpected by unfamiliar road users are present.
Standard:
05 If used, illuminated traffic signal signs shall be designed and mounted in such a manner as to avoid glare and reflections that seriously detract from the signal indications. Traffic control signal faces shall be given dominant position and brightness to maximize their priority in the overall display.
06 The minimum vertical clearance and horizontal offset of the total assembly of traffic signal signs (see Section 2B.53) shall comply with the provisions of Sections 4D.15 and 4D.16.
07 STOP signs shall not be used in conjunction with any traffic control signal operation, except in either of the following cases:
Support:
01 Pavement markings (see Part 3) that clearly communicate the operational plan of an intersection to road users play an important role in the effective operation of traffic control signals. By designating the number of lanes, the use of each lane, the length of additional lanes on the approach to an intersection, and the proper stopping points, the engineer can design the signal phasing and timing to best match the goals of the operational plan.
Guidance:
02 Pavement markings should be used at traffic control signal locations as provided in Part 3. If the road surface will not retain pavement markings, signs should be installed to provide the needed road user information.
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