The traffic lights are also known as traffic signals, traffic lamps, traffic semaphore, signal lights, stop lights, red lights (In the Southern United States), robots (in South Africa, Zimbabwe and other parts of Africa), and traffic control signals in technical parlance, are signaling devices positioned at road intersections, pedestrian crossings, and other locations to control flows of traffic.
The world's first traffic light was a manually operated gas-lit signal installed in London in December 1868. It exploded less than a month after it was implemented, injuring its policeman operator. Earnest Sirrine from Chicago patented the first automated traffic control system in 1910. It used the words "STOP" and "PROCEED", although neither word was illuminated.
Traffic lights alternate the right of way accorded to users by illuminating lamps or LEDs of standard colours (red, amber [yellow], and green) following a universal colour code. In the typical sequence of colour phases:
1. The green light allows traffic to proceed in the direction denoted, if it is safe to do so and there is room on the other side of the intersection.
2. The amber light warns that the signal is about to change to red. Actions required by drivers on a yellow light vary, with some jurisdictions requiring drivers to stop if it is safe to do so, and others allowing drivers to go through the intersection if safe to do so. A flashing amber indication is a warning signal
3. The red signal prohibits any traffic from proceeding. A flashing red indication requires traffic to stop and then proceed when safe (equivalent to a stop sign).
The traffic signals may go into a flashing mode if the conflict monitor detects a problem
Source: From Wikipedia, the free encyclopedia