Traffic lights, also known as traffic signals, traffic lamps, traffic semaphore, signal lights, stop lights and robots, and also known technically as traffic control signals are signalling devices positioned at road intersections, pedestrian crossings and other locations to control conflicting flows of traffic. The first manually operated gas-lit traffic light was installed in 1868 in London, though it was short-lived due to explosion. The first safe, automatic electric traffic lights were installed in the United States starting in the late 1890s.Traffic lights alternate the right of way accorded to road users by displaying lights of a standard color (red, yellow, and green) following a universal color code. In the typical sequence of color phases:
the green light allows traffic to proceed in the direction denoted, if it is safe to do so
the yellow (or amber) light warns that the signal will be changing from green to red (and from red to green in certain countries, such as in the UK[4]). Actions required by drivers on an amber 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 yellow indication is a warning signal
the red signal prohibits any traffic from proceeding
a flashing red indication is treated as a stop sign
In some countries traffic signals will go into a flashing mode if the controller detects a problem, such as a program that tries to display green lights to conflicting traffic. The signal may display flashing yellow to the main road and flashing red to the side road, or flashing red in all directions. Flashing operation can also be used during times of day when traffic is light, such as late at night.
