Speed cameras reduce the number of fatal and serious collisions in the areas they are installed in by more than a quarter, a UK study has found.
The Royal Automobile Club Foundation for Motoring (RAC) studied 551 fixed cameras in nine areas of England and found such incidents dropped by 27 per cent after cameras were set up.
However, the research also found that at 21 camera sites, the number of collisions increased. The foundation has written to 11 local authorities to suggest they examine whether the cameras should be moved.
Professor Stephen Glaister, director of the RAC, said a report it published in 2010 found that without speed cameras many more people would be killed or seriously injured each year.
He told the BBC: "Safety cameras are contentious, people dispute whether they work. But, in fact, the general public as a whole like them because they want these roads to be made safer.
"If cameras were turned off overnight there would be something like 80 extra people killed a year and 800 people killed or seriously injured. So the evidence is very good that on average they are effective."