As much as a traffic light is useful in smoothing out the traffic flow, the physical device by itself is not sufficient because people have to double check for safety everytime before they cross anyway. For example, when one crosses at as the green light comes on, one often double-checks to make sure that speeding car has come to a full stop. Obviously the light emits red/green light without seeing the actual traffic. In reality, sometimes a fast crazy car acts as a red light to a pedestrian, and other times a car in the distance is a green light.