Traffic lights, also known as traffic signals, traffic lamps, signal lights, robots and semaphores., are signalling devices positioned at or near road intersections, pedestrian crossings and other locations to control competing flows of traffic. Traffic lights were first installed in 1868 in London, United Kingdom; now used in almost every city of the world. Traffic lights alternate the right of way accorded to road users by displaying lights of a standard color (red, yellow/amber, and green) following a universal color code (and a precise sequence to enable comprehension by those who are color blind).
In the typical sequence of color phases:
- Illumination of the green light allows traffic to proceed in the direction denoted, if it is safe to do so
- Illumination of the orange/amber light denoting prepare to stop short of the intersection, if it is safe to do so
- Illumination of the red signal prohibits any traffic from proceeding
Usually, the red light contains some orange in its hue, and the green light contains some blue, said to be for the benefit of people with red-green color blindness.
Read more about Traffic Light: History, Lights For Public Transport, Turning Signals and Rules, Lane Control, Special Provisions, Dummy Lights, Implementation, US Department of Transportation Manual of Uniform Traffic Control Devices, Legal Implications, In Other Contexts, Gallery
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