where ever you see like a square impression in the road with cable stuff pushed into it(hope that makes sence)thats the point that sets the camera off,so if its at a set of lights withs both speeding and red light cameras they use the same point in the road to set them off,i've installed a hell of alot of speed cameras up the pacfic highway and i promise everyone here thats how they work.and im not 100% sure but i've heard only 70% of the cameras in nsw have any film in them at one time,so if u speed pass one and ur having a good day you might get away with it