Experts dispute speed cameras claim

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A statistical quirk meant that estimates of about 100 lives saved a year should be cut by half, according to researchers.

The assessment methods used to evaluate speed camera success failed to take account of random "bad luck" at notorious accident spots, it was claimed.

Dr Linda Mountain, from the University of Liverpool's Department of Engineering, said: "Although some parts of the road network are undoubtedly more dangerous than others, there is also a degree of randomness in where accidents occur - driver error, bad luck etc - which means that an accident can happen anywhere."

A study forming the basis of the Government claims looked at trends at all 4,100 camera sites in the UK.

It found that over a period of four years speed cameras were responsible for a 22% drop in the number of all accidents. The number of people killed or seriously injured was said to have fallen by 42%, amounting to around 100 lives saved a year.

Dr Mountain re-examined the evidence, conducting a new study looking at road accident numbers before and after cameras were installed at 215 sites.

This time an alternative analysis method was used called Empirical Bayes which took into account the element of uncertainty.

Allowing for the randomness element - known as "regression-to-the-mean" - showed a fall in accidents of 19%. Not allowing for this element would have indicated a reduction of 50%.

Speaking at the British Association Festival of Science at the University of Liverpool, Dr Mountain said: "I think it's not reasonable to say that 100 lives a year are being saved. I would have thought a smaller figure would be the correct one. The number has been overestimated by 50% on the basis of our data."