Which? cameras are not operating?
Which? magazine has reported that fewer than half of fixed safety cameras are operational at any one time (BBC News).
The consumer watchdog has calculated that 47% of cameras worked at any given moment in all 43 police authorities in England and Wales.
The Which? study also highlighted big regional differences, with all 60 cameras in Sussex working compared to just 10% of Lancashire's 287 sites.
Which? said that most areas rotated the working part of their cameras at random or in response to speed levels or accident statistics.
Martyn Hocking, Which? editor, said: "Safety cameras in some areas are always operational, whereas in others there could be a one in 10 chance the camera you've passed isn't working. It really is a tale of two counties."
Police authorities were asked how many safety camera housings they had and how many were operational under a Freedom of Information Act request.
A Which? survey of 1,920 members showed that they were divided over whether safety cameras made the roads safer, with 47% saying they did and 45% disagreeing.
Almost a quarter of those surveyed had received a penalty notice for speeding. Of these people, 48% paid more attention to driving within the speed limit following the fine, 39% were more cautious about their speed when near a camera and 18% did not change their driving.
Click here to read the full BBC News report.