Traffic lights, also known as traffic signals, stop lights, traffic lamps, stop-and-go lights, robots or semaphore, are signaling devices positioned at road intersections, pedestrian crossings, and other locations to control competing flows of traffic.
Traffic lights have been installed in most cities around the world to control the flow of traffic. They assign the right of way to road users by the use of lights in standard colors (Red - Amber - Green), using a universal color code (and a precise sequence, for those who are color blind). They are used at busy intersections to more evenly apportion delay to the various users.
The most common traffic lights consist of a set of three lights: red, yellow (officially amber), and green. When illuminated, the red light indicates for vehicles facing the light to stop; the amber indicates caution, either because lights are about to turn green or because lights are about to turn red; and the green light to proceed, if it is safe to do so.
Traffic lights have been installed in most cities around the world to control the flow of traffic. They assign the right of way to road users by the use of lights in standard colors (Red - Amber - Green), using a universal color code (and a precise sequence, for those who are color blind). They are used at busy intersections to more evenly apportion delay to the various users.
The most common traffic lights consist of a set of three lights: red, yellow (officially amber), and green. When illuminated, the red light indicates for vehicles facing the light to stop; the amber indicates caution, either because lights are about to turn green or because lights are about to turn red; and the green light to proceed, if it is safe to do so.
There are many variations in the use and legislation of traffic lights, depending on the customs of a country and the special needs of a particular intersection. There may, for example, be special lights for pedestrians, bicycles, buses, trams, etc; light sequences may differ; and there may be special rules, or sets of lights, for traffic turning in a particular direction. Complex intersections may use any combination of these.
Traffic light technology is constantly evolving with the aims of improving reliability, visibility, and efficiency of traffic flow.
The universal standard is for the red to be above the green, and if there is also an amber it is placed in the middle. If the three-set lights are mounted horizontally, the red will typically be to the left of the green. The standards apply whether the country drives on the left or the right, but the placement of the mountings on the road would be mirror images of the other.
Each country has differing road rules, including how traffic lights are to be interpreted. For example, in some countries, a flashing yellow light means that a motorist may proceed with care if the road is clear, giving way to pedestrians and to other road vehicles that may have priority (essentially the same as arriving at a non-signalized intersection and not facing a stop sign). A flashing red may be treated as a regular stop sign.
Traffic lights for pedestrians normally have two main lights: a red light that means 'stop' and a green light that means 'go' (or, more correctly, 'proceed with caution'). There is usually a flashing phase (red in the US and Australia, green in Europe) that means 'complete your crossing'. In most locales in North America, the colors used are a red-orange ("Portland orange") for "stop/wait" and a bluish-white ("lunar") for "go." While the "walk" signal is generally a walking human figure, North American pedestrian signals usually show an upraised hand for "stop," while most other countries display a standing human figure. Some older American signals display the verbal commands "Walk" (lunar white or green) and "Don't Walk" or "Wait" (red-orange).
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