Yes, we have those in the UK called SPECS (http://en.wikipedia.org/wiki/SPECS_%28speed_camera%29 http://en.wikipedia.org/wiki/SPECS_%28speed_camera%29) although

Yes, we have those in the UK called SPECS (http://en.wikipedia.org/wiki/SPECS_%28speed_camera%29 http://en.wikipedia.org/wiki/SPECS_%28speed_camera%29) although these are generally (only in my experience) used temporarily in roadworks etc. which have a temporary lower speed limit. I believe France did this the low-tech way in the past with toll roads (get a ticket with the time when you enter a toll road, pass it to the booth when you get off, S=D/T and caclulate if you have a speeding fine to pay as well)