Only half of all fixed speed cameras are actually switched on, police data has revealed.
Of the 45 police forces in the UK, four have no fixed speed cameras at all, while 13 said fewer than half of their cameras are active.
Out of a total 2,838 cameras in the UK, only 1,486 are in use, according to police responses to Freedom of Information requests.
But police said they regularly review which fixed cameras are turned on, meaning drivers should not be complacent.
Road safety charity Brake described the figures as concerning and called for all cameras to be switched on, while AA president Edmund King said the high number of inactive cameras was due to pressure on budgets.
Out of a total 2,838 cameras in the UK, only 1,486 are in use, according to police responses to Freedom of Information requests
Nine forces refused to disclose the information or failed to respond and the figures do not cover the mobile cameras that forces also use.
The forces with no active cameras are Cleveland, Durham, North Yorkshire and Northamptonshire, according to the Press Association, which uncovered the data.
The Northamptonshire force said it turned its cameras off in April 2011 but has kept them up just to deter speeding drivers.
Staffordshire Police oversee 272 fixed cameras but just 14 of them are active, while the Derbyshire force operates 112 cameras with just ten in operation.
The forces with a quarter or fewer switched on are West Yorkshire, Kent, South Yorkshire, Greater Manchester and Cheshire.
City of London, the Metropolitan Police/ Transport for London, Lancashire, Nottinghamshire, Suffolk and Northern Ireland said all their cameras were active.
A National Police Chiefs’ Council spokesman said the decision to use cameras was ‘an operational matter’, adding that ‘all forces have individual responsibility for their use of speed cameras’.
Mr King said: ‘Many of the empty yellow cases are due to cuts in road safety grants and the fact that digital cameras, although more effective, are very expensive. It is also reflective of the fact that proceeds from cameras are no longer allowed to be ring-fenced to be reinvested into yet more cameras as now all the money goes to the Treasury.’
He also warned motorists against gambling on a camera being inactive.
He said: ‘Drivers who play Russian roulette with fixed-site speed cameras are playing a dangerous game.
‘Our advice is stick to the limits rather than gambling on the yellow boxes.’
Four forces aren’t using any cameras at all – they are: Cleveland, Durham, North Yorkshire and Northamptonshire, according to the Press Association, which uncovered the data
But Claire Armstrong, co-founder of the lobby group Safe Speed, which campaigns for more traffic police officers rather than speed cameras, said the investigation ‘proves police forces don’t believe in cameras’.
She said: ‘Forces are conning the public into thinking cameras are there for road safety because, if they really thought that, every single one of them would be on.
‘They are a flawed road safety policy and the only way to truly improve that is with more traffic police officers on the roads.
‘I am glad there are only 52 per cent working – and we’d actually like to see less.’
However, Jason Wakeford, director of campaigns for road safety charity Brake, said: ‘A staggering 1,800 people lost their lives on British roads last year and speeding is a factor in thousands of crashes.
‘Speed cameras are a proven, cost-effective way of reducing deadly collisions and so it’s critical they are operational.’