In the United States, standard traffic lights rotate in a specific order; they change from green to yellow then red. The U.S. Department of Transportation notes that the timing sequence that guides the length of each segment is run by computers. Cameras on traffic lights impede standard light times.
The physical order of a conventional three-light signal is standard as well, with the red light on top, the yellow light in the middle and the green light on the bottom, according to Wikipedia. One reason to maintain a standard light sequence is to accommodate color blind drivers who cannot distinguish the colors, and must rely on the placement of each light.