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 competing 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: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.