In South Korea, this is taken to an extreme. Every freeway speed camera is indicated on the default Maps app. It beeps (shorter and louder as the camera gets closer) and then stops.

So everyone just slows down as their maps beep and speed up again once they pass the camera. But, I think this is accepted practice and my suspicion is that a lot of these cameras aren't even real.

Just by having them placed along the freeway every x metres, they force cars to constantly slow down.