Editing Traffic light (section)

== Public transport signals ==
Traffic lights for public transport often use signals that are distinct from those for private traffic. They can be letters, arrows or bars of white or (an LED 100-[[watt]] typical) coloured light.

=== Transit signals in North America ===
{|class="wikitable"
|+MUTCD Fig. 8C-3
! colspan=5 | Three-lens signal !! colspan=6 | Two-lens signal
|-
! rowspan=3 | [[File:8C-3 (Light Rail 1).svg|frameless|upright=0.2]]<br />Single LRT route
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
| colspan=5 | &nbsp;
|-
| Prepare to stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail CAUTION).svg|frameless|upright=0.1]] || style="background:#aaa;" | || (flashing)
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
|-
| Go || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
| Go || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | || {{efn-lr|name=2prep|"Go" lens may be used in flashing mode to indicate "prepare to stop"}}
|-
| style="font-size:25%;background:#888;" colspan=11 | &nbsp;
|-
! rowspan=3 | [[File:8C-3 (Light Rail 2R).svg|frameless|upright=0.2]]<br />Two LRT route diversion
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
| colspan=5 | &nbsp;
|-
| Prepare to stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail CAUTION).svg|frameless|upright=0.1]] || style="background:#aaa;" | || (flashing)
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
|-
| Go || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-R).svg|frameless|upright=0.1]] || {{efn-lr|name=samehouse|Could be in single housing}}
| Go || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-R).svg|frameless|upright=0.1]] || {{efn-lr|name=2prep}}{{efn-lr|name=samehouse}}
|-
| style="font-size:10%;background:#888;" colspan=11 | &nbsp;
|-
! rowspan=3 | [[File:8C-3 (Light Rail 2L).svg|frameless|upright=0.2]]<br />Two LRT route diversion
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
| colspan=5 | &nbsp;
|-
| Prepare to stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail CAUTION).svg|frameless|upright=0.1]] || style="background:#aaa;" | || (flashing)
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
|-
| Go || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-L).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | || {{efn-lr|name=samehouse}}
| Go || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-L).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | || {{efn-lr|name=2prep}}{{efn-lr|name=samehouse}}
|-
| style="font-size:25%;background:#888;" colspan=11 | &nbsp;
|-
! rowspan=3 | [[File:8C-3 (Light Rail 3LR).svg|frameless|upright=0.2]]<br />Three LRT route diversion
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
| colspan=5 | &nbsp;
|-
| Prepare to stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail CAUTION).svg|frameless|upright=0.1]] || style="background:#aaa;" | || (flashing)
| Stop || style="background:#aaa;" | || style="background:#aaa;" | [[File:8C-3 (Light Rail STOP).svg|frameless|upright=0.1]] || style="background:#aaa;" | ||
|-
| Go || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-L).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-R).svg|frameless|upright=0.1]] || {{efn-lr|name=samehouse}}
| Go || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-L).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail GO).svg|frameless|upright=0.1]] || style="background:#aaa;" | [[File:8C-3 (Light Rail DIV-R).svg|frameless|upright=0.1]] || {{efn-lr|name=2prep}}{{efn-lr|name=samehouse}}
|-
| colspan=11 style="text-align:left;" | '''Notes'''<br />{{notelist-lr}}
|}
[[MUTCD]] specifies a standard vertically oriented signal with either two or three lenses, displaying white lines on a black background.<ref>{{MUTCD |year=2009 |revision=3 |chapter=8C}}</ref>{{rp|Fig.8C-3}}

Some systems use the letter B for buses and T for trams. The [[METRO (Minnesota)|METRO]] light rail system in [[Minneapolis, Minnesota]], the [[Valley Metro Rail]] in [[Phoenix, Arizona]]. The [[New Orleans Regional Transit Authority|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.

=== Public transport signals in Europe ===
In some European countries and [[Russia]], dedicated traffic signals for public transport (tram, as well any that is using a [[bus lane|dedicated lane]]) [[s:ru:Правила дорожного движения Российской Федерации#6. Сигналы светофора и регулировщика|have]] four white lights that form the letter T.{{Citation needed|date=December 2009}} 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.<ref>{{Cite web|url=http://www.trafikverket.se/TrvSeFiler/Foretag/Bygga_och_underhalla/Vag/Vagutformning/Dokument_vag_och_gatuutformning/Vagar_och_gators_utformning/Trafiksignaler/04_utrustning_trafiksignaler.pdf|title=Publication on traffic lights the from the Swedish Transport Administration|access-date=25 August 2011|archive-date=23 September 2016|archive-url=https://web.archive.org/web/20160923032057/http://www.trafikverket.se/TrvSeFiler/Foretag/Bygga_och_underhalla/Vag/Vagutformning/Dokument_vag_och_gatuutformning/Vagar_och_gators_utformning/Trafiksignaler/04_utrustning_trafiksignaler.pdf|url-status=dead}}</ref> In Sweden, All signals use white lighting and special symbols ("S", "–" and an arrow) to distinguish them from regular signals.

[[File:Public_transportation_traffic_lights_in_NL_and_BE.svg|thumb|Tram signals in Netherlands (top), Belgium, Luxembourg, France, and Germany (bottom)]]
The [[Netherlands]] uses a distinctive "negenoog" (nine-eyed) design shown on the top row of the diagram.<ref>{{in lang|nl}} [http://wetten.overheid.nl/cgi-bin/deeplink/law1/title=RVV RVV 1990 artikel 70] Official regulation of traffic rules and traffic signs</ref> 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").

=== Public transport signals in the Asia-Pacific region ===

In Japan, tram signals are under the regular vehicle signal; however, the colour of the signal intended for trams is orange("yellow"). 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. 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.<gallery>
File:HK Causeway Bay tram traffic lights Aug-2017.jpg|T signal (trams) in Hong Kong
File:Karlsruhe Ebertstr-Karlstr Tramampeln.jpg|Bus and tram signals in [[Karlsruhe]], [[Germany]]
</gallery>

=== Preemption and priority ===
{{Main|Traffic signal preemption|Bus priority}}

Some regions have signals that are interruptible, giving priority to special traffic, usually [[emergency vehicle]]s such as [[firefighting apparatus]], [[ambulance]]s, and [[police car]]s.<ref>{{cite web |title=Emergency vehicle traffic signal preemption system |work=United States Patent and Trademark Office |url=http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=6326903 |access-date=7 October 2005 |archive-date=21 December 2016 |archive-url=https://web.archive.org/web/20161221033705/http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=6326903 |url-status=dead }}</ref><ref>{{cite web|url=https://mutcd.fhwa.dot.gov/HTM/2003r1/part4/part4f.htm|title=FHWA – MUTCD – 2003 Edition Revision 1 Chapter 4F|work=dot.gov}}</ref> 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. 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.<ref>{{cite web|title=Emergency Vehicles at Red Signal or Stop Sign|url=http://codes.ohio.gov/orc/4511.03|website=Ohio Laws and Rules|access-date=22 July 2014}}</ref><ref>{{cite web|title=Emergency Service and Vehicles|url=https://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+46.2-920|website=Virginia General Assembly|access-date=22 July 2014}}</ref>

Unlike preemption, which immediately interrupts a signal's normal operation to serve the preempting vehicle and is usually reserved for emergency use, "[[Bus priority|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.