Editing Traffic light (section)

===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}}}}