[dangrossman]

Near my home (southeastern Pennsylvania), if you pull up to an intersection and there's no traffic in the opposing direction, the light changes so you get a near-immediate green. It works great at night when nobody else is near the intersections.

I noticed the same thing when I lived in Seattle for a few months.

I doubt the signals are communicating with each other, but there is definitely some deployment of signals with sensors to detect whether a car is waiting on each side of the intersection.