Editing Traffic light (section)

==Vehicular signals==
[[File:Traffic lights.jpg|thumb|right|Traffic lights can have several additional lights for filter turns or bus lanes.]]

[[File:Sumburgh Airport Barrier.webm|thumb|Road crossing of [[A970 road|A970]] with [[Sumburgh Airport]]'s runway in [[Shetland]]. The movable barrier closes when an aircraft lands or takes off.]] [[File:Japanese signal aokibashi.jpg|thumb|Horizontally-mounted signals in Japan]]A set of lights, known as a signal head,<ref name=":1">[https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/851465/dft-traffic-signs-manual-chapter-6.pdf Traffic Signs Manual – Chapter 6: Traffic Control]. ''Department for Transport, Department for Infrastructure (Northern Ireland), Transport Scotland and Welsh Government''. Accessed: 18 December 2021.</ref>{{Rp|location=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.

=== Meanings of signals ===
The [[Vienna Convention on Road Signs and Signals|1968 Vienna Convention on Road Signs and Signals]] Chapter III provides international standards for the setup of traffic signal operations. Not all states have ratified the convention. A three-colour signal head should have three non-flashing lights which are red, [[amber (color)|amber]], and green, arranged either horizontally (on the side opposite to the direction of traffic){{clarify|date=May 2025}} 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.<ref name=":5" /> Permissible signals for regulating vehicle traffic (other than public transport vehicles) are outlined in Article 23:<ref name=":5" />
{| class="wikitable"
|+Standard meanings for traffic lights internationally (Vienna Convention, Article 23)
! colspan="2" |Light type
!Meaning
|-
| rowspan="4" |Non-flashing
|width=80|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 rule continues to apply.
|-
|[[amber (color)|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.
|-
| rowspan="2" |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 caution.
|}
Green arrows are added to signals to indicate that traffic can proceed in a particular direction while the main lights for that approach are red, or that traffic can only proceed 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").<ref name=":1" />{{Rp|location=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.<ref>{{Cite web |title=Flashing Yellow Arrow Traffic Signals – Traffic Engineering – MnDOT |url=https://www.dot.state.mn.us/trafficeng/signals/flashingyellowarrow.html |access-date=18 December 2021 |website=www.dot.state.mn.us}}</ref>

==== Green arrows ====
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.<ref name=":1" />{{Rp|location=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|date=December 2021}} 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.<ref name=":1" />{{Rp|location=3.5}}

Some variations of this setup exist. One version is a horizontal bar with five lights&nbsp;– 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.<ref>{{Cite web |title=MUTCD 11th Edition - Part 4 |url=https://mutcd.fhwa.dot.gov/pdfs/11th_Edition/part4.pdf |access-date=13 December 2024 |website=[[Federal Highway Administration]]}}</ref> 

A third type is known as a "doghouse" or "cluster head"&nbsp;– 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|date=December 2021}} 

In a fourth type, sometimes seen at intersections in [[Ontario]] and [[Quebec]], Canada, there is no dedicated left-turn lamp per se.<ref>{{cite web |title=RoadSense for Drivers&nbsp;– Signs, Signals and Road Markings |url=http://www.icbc.com/driver-licensing/Getting-licensed/drivers3.pdf |url-status=dead |archive-url=https://web.archive.org/web/20131022032056/http://www.icbc.com/driver-licensing/Getting-licensed/drivers3.pdf |archive-date=22 October 2013}} Accessed: 25 March 2014</ref><ref>{{Cite book |title=Ontario Traffic Manual Book 12: Traffic Signals. |publisher=Ministry of Transportation of Ontario |year=2012 |pages=55}}</ref> 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 can cause confusion amongst visitors to British Columbia, where a flashing green signal denotes a pedestrian-controlled crosswalk.<ref>{{Cite news |last=Tchir |first=Jason |date=June 23, 2015 |title=Why B.C.'s flashing green lights don't mean the same thing as those in Ontario |url=https://www.theglobeandmail.com/globe-drive/culture/commuting/why-bcs-flashing-green-lights-dont-mean-the-same-thing-as-those-in-ontario/article25066266/ |url-status=live |archive-url=https://web.archive.org/web/20241214013728/https://www.theglobeandmail.com/globe-drive/culture/commuting/why-bcs-flashing-green-lights-dont-mean-the-same-thing-as-those-in-ontario/article25066266/ |archive-date=December 14, 2024 |access-date=April 21, 2025 |work=[[The Globe and Mail]]}}</ref> For this reason, Ontario is phasing out the use of flashing green signals and instead replacing them with arrows.<ref>{{cite web |title=RoadSense for Drivers&nbsp;– Signs, Signals and Road Markings |url=http://www.icbc.com/driver-licensing/Getting-licensed/drivers3.pdf |url-status=dead |archive-url=https://web.archive.org/web/20131022032056/http://www.icbc.com/driver-licensing/Getting-licensed/drivers3.pdf |archive-date=22 October 2013}} Accessed: 25 March 2014</ref><ref>{{Cite book |title=Ontario Traffic Manual Book 12: Traffic Signals. |publisher=Ministry of Transportation of Ontario |year=2012 |pages=55}}</ref>

==== Countdown lights ====
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 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:

# Lights have not counted down, when 99 seconds are left, start counting. During the standby time, the light may be displayed as "99", "00", "--" or not displayed.
# Last 2 digits count light of the timeout (the counter light is 15 while the time is 115 seconds, there are some types of lights that count as "-9" or "9-" when the time is 109 seconds)
# Tens digit on the displayer becomes a letter. Displaying A0 for 100 seconds, B0 for 110 seconds, so forth.
# Displaying only last 2 digits but with flashing to indicate it's more than 100.
[[File:CountDownTrafficLight.gif|thumb|125px|A countdown light]]

==== Issue about yellow light dilemma zone in South Korea  ====
In South Korea, the yellow (amber) light dilemma zone is not legally recognized. In other words, when the amber light is on, traffic may not pass the stop line or enter the intersection, even if the traffic cannot safely stop when the light shows.

In May 2024, this was reaffirmed by the [[Supreme Court of Korea]] ,<ref>{{cite web|title=Supreme Court rules that driver should stop when yellow light turns on even if car is expected to stop in intersection|url=https://english.khan.co.kr/khan_art_view.html?artid=202405141817347&code=710100|editor=The Kyunghyang Shinmun|date=2024-05-14}}</ref><ref>{{cite web|language=ko|script-title=ko:'갈까 말까' 딜레마존…"안 겪어보면 몰라" 판결에 분통 [사실은]|url=https://news.sbs.co.kr/news/endPage.do?news_id=N1007656713|editor=SBS|date=2024-05-22}}</ref> for a case where the driver was speeding at 62&nbsp;km/h in a street limited up to 40&nbsp;km/h, {{#expr: ((62/40)-1)*100 round 0}} % higher than the allowed speed.<ref>{{Cite web |date=2024-05-13 |title=The Supreme Court ruled that if a yellow light is turned on at the traffic light just before enterin.. - MK |url=https://www.mk.co.kr/en/society/11014731 |access-date=2024-10-11 |website=[[Maeil Business Newspaper]] |language=en}}</ref>{{Unreliable source?|reason=The English version of this website uses automatic machine translation; see [[WP:KO/RS]]|date=November 2024}}

Criticism in South Korea says that this is unrealistic and unreasonable. This can cause multiple collisions due to sudden braking.

In 2016, when speed limit was up to 60&nbsp;km/h, proposed alternatives to this kind of collision were only roundabouts, speed compliance increase and speed practice reduction or elderly zones are also proposed solutions.<ref>{{Cite web| title=Halving the Number of Road Deaths in Korea | url=https://www.itf-oecd.org/sites/default/files/docs/halving-road-deaths-korea.pdf | archive-url=https://web.archive.org/web/20210117155137/https://www.itf-oecd.org/sites/default/files/docs/halving-road-deaths-korea.pdf | archive-date=2021-01-17}}</ref>

=== Yellow trap ===
Without an all-red phase, cross-turning traffic may be caught in a '[[yellow trap]]'. When the signal turns yellow (amber), 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.<ref>{{Cite web |title=Frequently Asked Questions – Part 4 Highway Traffic Signals – FHWA MUTCD |url=https://mutcd.fhwa.dot.gov/knowledge/faqs/faq_part4.htm#tcsfq3 |access-date=18 December 2021 |website=[[Federal Highway Administration|Federal Highway Administration (FHWA)]]}}</ref>  This can also happen when emergency vehicles or railroads preempt normal signal operation.
<ref>{{cite web |date=7 January 2015 |title=The Flashing Yellow Arrow and the Yellow Trap |url=https://streets.mn/2015/01/07/the-flashing-yellow-arrow-and-the-yellow-trap/ |access-date=3 April 2019}}</ref> 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.<ref>{{cite web |title=FHWA&nbsp;– MUTCD&nbsp;– 2003 Edition Revision 1 Chapter 4D |url=https://mutcd.fhwa.dot.gov/htm/2003r1r2/part4/part4d.htm#section4D05 |access-date=19 May 2009 |publisher=[[Federal Highway Administration|Federal Highway Administration (FHWA)]]}}</ref><ref>{{cite web |title=FHWA&nbsp;– MUTCD&nbsp;– 2003 Edition Revision 1 Chapter 2C |url=https://mutcd.fhwa.dot.gov/htm/2003r1r2/part2/part2c.htm#section2C39 |access-date=19 May 2009 |publisher=[[Federal Highway Administration|Federal Highway Administration (FHWA)]]}}</ref>

===Variations===
{{Main|Variations in traffic light operation}}The United States is not party to the [[Vienna Convention on Road Signs and Signals|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. 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).<ref name=":6">2009. [https://mutcd.fhwa.dot.gov/pdfs/2009r1r2/part4.pdf Manual on Uniform Traffic Control Devices for Streets and Highways: Chapter 4]. US Federal Highway Administration. URL Accessed: 7 January 2022.</ref> 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.<ref name=":6" /> {{anchor|Intersection control beacon}}Flashing red or amber lights, known as ''intersection control beacons'', are used to reinforce stop signs at intersections.<ref>{{cite book |title=Manual on Uniform Traffic Control Devices |title-link=Manual on Uniform Traffic Control Devices |date=2009 |publisher=Federal Highway Administration |chapter=Section 4L.02 Intersection Control Beacon |chapter-url=https://mutcd.fhwa.dot.gov/htm/2009/part4/part4l.htm#section4L02}}</ref> The MUTCD specifies the following vehicular signals:<ref name=":6" />
{| class="wikitable mw-collapsible mw-collapsed"
|+Standard meanings for traffic lights in the United States (MUTCD, Chapter 4)
!Signal
!Meaning (steady)
!Meaning (flashing)
|-
![[File:MUTCD 4D-2 (Circular Green).svg|frameless|upright=0.2]]<br />Circular green
|Traffic can proceed in any permitted direction, yielding to pedestrians in a crosswalk or other vehicles when turning
| rowspan="2" |Not to be used
|-
![[File:MUTCD 4D-2 (Green Arrow LEFT).svg|frameless|upright=0.2]]<br />Green arrow
|Traffic can proceed in the direction shown by the arrow, yielding to any pedestrians in a crosswalk or other vehicles in the intersection
|-
![[File:MUTCD 4D-2 (Circular Yellow).svg|frameless|upright=0.2]]<br />Circular yellow
|The green movement is being terminated and a red signal will soon be displayed
|Traffic can cautiously enter the intersection, yielding to pedestrians and other vehicles
|-
![[File:MUTCD 4D-2 (Yellow Arrow LEFT).svg|frameless|upright=0.2]]<br />Yellow arrow
|The green or flashing arrow movement is being terminated
|Traffic can cautiously enter the intersection to make the movement displayed by the arrow, yielding to pedestrians and other vehicles
|-
![[File:MUTCD 4D-2 (Circular Red).svg|frameless|upright=0.2]]<br />Circular red
|Unless another signal permits, traffic shall not enter the intersection except to lawfully [[turn on red]]
|Traffic must stop before entering the intersection, but may then treat the signal by the same rules as a STOP sign.
|-
![[File:MUTCD 4D-2 (Red Arrow LEFT).svg|frameless|upright=0.2]]<br />Red arrow
|Traffic shall not make the movement displayed by the arrow
|Traffic must stop before entering the intersection, but may then treat the signal by the same rules as a stop sign to make the movement displayed by the arrow.
|}[[File:Colourblind traffic signal.JPG|thumb|A traffic signal in [[Halifax Regional Municipality|Halifax]], [[Nova Scotia]], with specially shaped lights to assist people with colour blindness]]
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.<ref>{{cite web|title=Traffic Signals|url=http://cityofcarrollton.com/index.aspx?page=259|archive-url=https://web.archive.org/web/20100113150357/http://cityofcarrollton.com/index.aspx?page=259|url-status=dead|archive-date=13 January 2010|website=Carrollton Texas|access-date=12 July 2014}}</ref> 

Japanese traffic signals mostly follow the same rule except that the green "go" signals are referred to as 青 (ao), typically translated as "blue", reflecting [[Blue–green distinction in language#Japanese|a historical change in the Japanese language]]. As a result, Japanese officials decreed in 1973 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.<ref>{{cite news|url=http://www.japantimes.co.jp/life/2013/02/25/language/the-japanese-traffic-light-blues-stop-on-red-go-on-what/#.WRmAuuWGNPZ|title=The Japanese traffic light blues: Stop on red, go on what|first=Peter|last=Backhaus|date=25 February 2013|work=The Japan Times|access-date=14 July 2017}}</ref>

In the UK, normal traffic lights follow this sequence:<ref>{{cite web|url=http://www.legislation.gov.uk/uksi/2016/362/schedule/14/made|title=The Traffic Signs Regulations and General Directions 2016|date=2016|publisher=The National Archives|website=legislation.gov.uk|access-date=14 July 2017}}</ref>
* Red – Stop, do not proceed.
* Red and amber – Get ready to proceed, but do not proceed yet.
* Green – Proceed if the intersection or crossing is clear; vehicles are not allowed to block the intersection or crossing.
* Amber – Stop, unless it is unsafe to do so.
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<ref>{{Cite book|author=Forschungsgesellschaft für Straßen- und Verkehrswesen|title=Begriffsbestimmungen, Teil: Verkehrsplanung, Straßenentwurf und Straßenbetrieb|publisher=FGSV Verlag|year=2000|pages=81}}</ref> and avoid a stop due to reaching the intersection when lights are red.<ref>{{Cite book|author=Andreas Richter|title=Geschwindigkeitsvorgabe an Lichtsignalanlagen|publisher=DUV|year=2005|isbn=3-8244-0828-7|pages=33–34}}</ref>{{efn|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.{{Clarify|reason=See note|date=July 2020}}}}