it would also be relatively straightforward to require cars to self-report speeding (keep a speed/position log, have it be read out at annual inspection). There are some issues around tunnels and poor GPS geolocation in urban areas, but it would work great for things like highways...
I had that exact thought as I was typing my post! :D
That said, I can see many reasons that is not liked. Amusingly, as you add more and more detection systems to cars for stuff like this, you are backing into autonomous vehicles.
Detecting out of spec driving is a much simpler (and cheaper to solve) problem than autonomous driving, and may have higher safety benefits? Yes there are privacy concerns but the same concerns exist with autonomous driving.
