Traffic light signalling

The use of traffic lights to control the movement of traffic differs regionally and internationally in certain respects. This article describes some of these non-universal features. Note that the color phase commonly known as "yellow" is often referred to, especially in official usage, as "amber"; for consistency this article uses "yellow" throughout.

In the United States, a flashing red light is the equivalent of a stop sign. In the United States and Australia, flashing yellow does not require traffic to stop, but drivers should exercise caution since opposing traffic may enter the intersection after stopping. This may be used when there is a malfunction with the signals, or late at night when there is little traffic. A single four-way flashing light showing only one color in each direction may be used at intersections where full three-color operation is not needed, but stop or yield signs alone have not had acceptable safety performance. Yellow lights are displayed to the main road, to highlight the intersection and inform drivers of the need for caution. Red lights supplement stop signs on the side road approaches. All-way red flashing lights can supplement all-way stop control, but all-way yellow beacons are prohibited by United States regulations.

In New Zealand, paired red/red traffic lights are often installed outside Fire and Ambulance Stations on major roads, which when activated by the station, flash alternatively (so that at any time one red light is always showing), the purpose being to cause to traffic to stop for a set amount of time to allow emergency vehicles to exit their station safely.

In some parts of Canada, a flashing green (known as Advanced Green) light signals permission for a left turn before the opposing traffic is allowed to enter the intersection, i.e., oncoming traffic is facing a RED light. Similarly, a flashing green may be an Extended Green, for left turns after the opposing traffic's full green phase. The flashing light may be a "full" green, or a green left arrow, both meaning the same thing. At least one traffic light in Montreal (on the Island of Montreal, 'Right-on-Red' is not allowed), has a flashing right-turn arrow, indicating that the pedestrian crossing has a red light, so it is safe to turn right and drive across it. At some intersections in Winnipeg, Manitoba, a flashing green right-turn arrow appears with a red light when traffic from the right has a green flashing left-turn arrow and is not allowed to make a U-turn. In other parts of the same country (e.g., Vancouver) a flashing green light conveys a very different meaning: the crossing road has stop signs with no lights of its own, and oncoming traffic also has a flashing green, not a red stop-light. This functions the same as a European "priority" sign (a yellow-and-white diamond shaped sign indicating that the current street is a Priority or "main" road, which cross streets must yield to at uncontrolled junctions, opposite to the usual arrangement in many European countries), for which there is no direct equivalent in North America.

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