Are speed cameras really a deterrent?
BBC Radio 4's More or Less was broadcast on Thursday, 29 January, 2004 at 1500 GMT.
Do speed cameras reduce the number of accidents?
If you were in charge of road safety in your county and you had the money to pay for one speed camera, where would you put it?
In the spot with the most speed related accidents perhaps?
And if the number of accidents then fell dramatically would that be proof that the speed camera had improved safety?
Well according to the pressure group, Safe Speed, it would prove no such thing.
They say that the reduction could be due to what statisticians call "regression to the mean".
In other words that if the occurrence of something is abnormally high or abnormally low simply because of random variation, the statistical chances are that it will be much closer to the average the next time you measure it.
But are accident black spots simply the result of random variation or are there some areas where speeding is a particular danger?
And should the Department for Transport's claim that speed cameras have been shown to cut accidents by around 35% have taken regression to the mean into account?
More or Less attempts to get to the truth about speedcams.
Producer: Michael Blastland
Editor: Nicola Meyrick