If the government wanted to stop speeding they could adopt, and slightly modifiy, a system used here in Portugal (the death rate in Portugal is 6 times more than the UK). You have speed cameras conected to traffic lights further down the road. If the camera see you are going to fast it changes the lights to red. Therefore, if you speed you do not gain from it. The only problem with the system over here is there are no traffic light cameras so many people just jump the lights. So add cameras to catch people who jump the red lights and you will have a good system.
Of course that wont make any money though.