Stop Go

You're standing on the curb, waiting to cross the street. A red man stands facing you from the traffic island (your mileage may vary). You press the knob and wait for him to become a green, walking man. On the other side of the street, a girl is waiting in the exact same position. For some reason, she has her own set of guys, facing her, with their own red and green lightbulbs. Why not have one traffic light, facing both ways, with two lightbulbs in it? It may sound hopelessly trivial, but how many pedestrian traffic lights are there?