Question: how do speed cameras know if ur going fast?

Pete Etchells answered on 24 May 2012:

Good question! It depends on the type of speed camera. The big yellow ones, called GATSO cameras, usually are accompanied by white lines on the road. The camera takes two photos, about half a second apart, and compares where you are in relation to the white lines to see if you’re going too fast.

Another type of camera relies on sensors that are built into the road, and uses an onboard computer to calculate how fast you travelled between two points in the road.

I’m not so sure about how mobile camera unit. I *think* what happens is that they shine a laser at your car, which bounces back to the camera. if you do this twice in quick succession on a car that’s coming towards you, then the second laser will get bounced back faster than the first (because it’s travelling over a shorter distance). I guess they have a computer that uses this to work out how fast you’re travelling!