It's not that difficult to drive at a constant speed. It's one of the basic things you learn before passing your driving test. If you can't do that (law abiding or not) then you shouldn't be on the road. Furthermore it takes a nano second to glance at your speedo. To argue a picture of drivers gripping the steering wheel white knuckled, weaving all over the road and too scared to take their eye of the clock is nonsensical. By far the vast majority of drivers can see the GATSO in advance and slow down accordingly. Yes they might well speed up again, but if it is placed strategically within an accident hot spot it will reduce accidents. What it won't stop are the unregistered, uninsured drivers who deliberately flout the law on and off the road with little chance of getting caught.