Around half of all fixed speed cameras on British roads are switched off, according to new data.
Figures obtained by the Press Association from 36 of the 45 police forces in the UK revealed that four have no fixed speed cameras working at all and 13 have fewer than half actively catching speeding drivers.
Out of a total 2,838 cameras, only 1,486 (52%) are active.
Police forces with all their fixed speed cameras switched on include the City of London, the Metropolitan Police/Transport for London, Lancashire, Nottinghamshire, Suffolk and Northern Ireland.
However, Northamptonshire said it turned off its fixed speed cameras in 2011, but left the structures in place to deter speeding. Cleveland, Durham and North Yorkshire also admitted that none of their fixed cameras were working.
Meanwhile, Staffordshire has 272 cameras across its region but only 14 are active, and Derbyshire has 112 cameras, of which only 10 are switched on.
The figures do not include mobile speed cameras that forces also use.
Edmund King, president of the AA, said: "It has long been the case that cameras were moved between sites, depending on need. When it comes to the chances of being caught on camera, it is a postcode lottery. All cameras in City of London and Suffolk are working whereas only 5% are active in Staffordshire."
"However, drivers should remember that lack of a yellow fixed camera doesn't mean they are immune from mobile hidden cameras. Best advice is stick to the limits rather than gambling on the yellow boxes."
Jason Wakeford, director of campaigns for road safety charity Brake, pointed out that 1,800 people lost their lives on British roads last year and speeding is a factor many crashes.
"Speed cameras are a proven, cost-effective way of reducing deadly collisions and so it's critical they are operational," he added. "We are concerned to see figures which suggest so many are switched off and would urge they are urgently put back into action."
Do you think fixed speed cameras are an effective deterrent?