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Transportation engineers working for DOT or contractors for DOT are responsible for timing based on traffic flow and traffic studies. transportation engineers fall under the civil engineering discipline... for the most part red and yellow times are mathematical based on reaction time, intersection length, and the speed limit. green time varies based on the traffic studies presented at the time the lights were installed and sometimes projected future growth.
That being said the use of sensors in the road and cameras can adjust green times for specific times of day to make the lights more driver friendly. The biggest problem IMO is the lack of continuity between intersections, each one typically acts as its own entity. Engineers recognize this and will attempt to design streets with a "green wave". Once a driver hits one light, the remaining lights on that route will be green, if the driver continues at the posted speed limit. I'd like to go on further but i dont think its necessary.
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