The Government has over-estimated the value of speed cameras as traffic safety measures used in preventing death and injury, according to a study.
Researchers from the University of Liverpool said a statistical quirk meant claims of about 100 lives saved a year should be cut by half.
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'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 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 conducted a new study looking at road accident numbers before and after cameras were installed at 215 sites.
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%.
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