Few drivers know this, but there are specific distances between the radar signs and the devices themselves.
Although we see many of them on the side of the road, the signs to indicate the proximity of a speed camera do not always have the desired effect. Supposed to warn that a device is going to check the speed of their vehicles a few meters further, they have the gift of provoking a sort of panic among some motorists who, upon seeing them, use and abuse the brake pedal. Result: a slowdown is created and that is how we see traffic jams forming, especially when traffic is already dense.
All this would not happen if drivers knew how far these road signs were from the speed cameras and the speed cameras themselves. Not to mention that it would help them know at what precise moment to check their speed or even slow down to avoid being caught speeding and having to pay a fine, most often accompanied by the loss of points on their driving license. Because the distance between the sign and the speed control device is almost always the same in France, give or take a few meters, depending on the type of road on which it is installed.
In fact, the higher the speed limit on the road, the greater the distance. On roads limited to 70 km/h, you have to allow 300 meters between the sign and the radar. It is 400 meters on roads at 80 or 90 km/h when the gap climbs to 600 meters on motorways. Concretely, at a speed of 130 km/h on a motorway, you can let about fifteen seconds pass, between 16 and 17 to be precise, between the sight of the sign and the place where the speed of your vehicle will be measured. You should know that the distance can vary by around fifty meters depending on the environment. Also, when a radar is installed in a city, it is most often at the entrance to the city that the signs “Frequent radar controls” or “Automatic controls” are established and not at a precise distance from the radar(s).
Since you may not always be focused on your GPS or Smartphone when driving, and therefore miss certain alerts, knowing how many meters away the radar is once you pass in front of the warning sign can be useful. In France, there is no law requiring you to report the proximity of a radar. But government services have chosen to install a sign before each automatic speed control radar. This is probably a way to calm (a little) the discontent of motorists who have seen these devices spring up like mushrooms on the sides of the roads in about twenty years.
While fixed speed cameras are reported, this is not the case for mobile speed cameras on board police or private company vehicles, nor for red light cameras. But the best thing to do to avoid the risk of being flashed is obviously to respect the speed limits everywhere and all the time.