Traffic Lights

sTraffic lights, also known as traffic signals, traffic lamps, signal lights, robots in South Africa[1] and, in the past, semaphores,[2] are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic. Traffic lights were first installed in 1868 in London[3] and are now used all over 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. 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/amber light denoting prepare to stop short of the intersection, if it is safe to do so * the red signal prohibits any traffic from proceeding
Failure to obey traffic lights is a crime everywhere.
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Types
Single aspects
The simplest traffic light comprises either a single or a pair of colored aspects that warns any user of the shared right of way of a possible conflict or danger.
Dual aspects
These are often seen at railway crossings and at intersections of streets. They flash yellow when cross traffic is not expected, and turn red to stop traffic when cross traffic occurs. They are also used on ramp metering, where motorists enter a freeway in heavy traffic. Only one driver per lane goes per green.
Three or more aspects
The standard is the red light above the green, with yellow between. (And railroad signals are intentionally the opposite: with green on top and red on the bottom so that the two types can't be confused.[citation needed]) When sideways, the arrangement depends on the rule of the road. In right-lane countries, the green light is on the right, and in left-lane countries, the left.
Sounds
In some jurisdictions such as Australia and Ireland pedestrian lights are associated with a sound device, for the benefit