There were some workers doing maintenance on the signal control box at the intersection near our house and one of them was kind enough to explain it all to us.
It was all v.v. interesting.
They can actually dial into the computer at the top there from a remote location and change the timing of the lights, advances and everything! The folder on the right contains all the rules and regs, and all the wires on the bottom are the ones that connect to the actual lights. (pedestrian signals too!) There are even sensors buried under the road that are weight sensitive, that can trigger an advance left turn signal.
It's really true, having kids does make you smarter!!!!