Most likely it's camera based, using the license plate. We have something similar in Australia that is used for trucks but not cars (so far). One of the side

Most likely it's camera based, using the license plate. We have something similar in Australia that is used for trucks but not cars (so far). One of the side effects of Google completely mapping the developed countries has been a comprehensive map of the speed limits - if you use Waze it already warns you when you're exceeding the limit by changing the colour of the speed icon. I actually find it pretty handy on the highways here.