In Phoenix (and perhaps elsewhere), at many 3-way intersection, the green light for any of the crossing streets will not come on unless a sensor detects there is a car waiting to proceed. Not only must there be a car there, but it has to be close enough to the line to be picked up by the sensor. If you have a lunch appointment and are behind a car that is not close enough to the line, after your light doesn't turn green as the other two streets go through three cycles, you should realize the problem. Merely, honking at the car ahead will do no good because the driver will think, as he points to the red light, you're asking him to go through a red light. After you see that 6 cars behind you are becoming frustrated, although it involves putting yourself at great risk, you might jump out of your car, knock on the driver side window of the car ahead, and politely explain the problem first using your words and then, if necessary, with hand gestures.