Scotland's safety camera partnerships - which operate speed cameras in conjunction with local police, councils and other authorities - run 169 roadside speed cameras across the country.
But statistics released under freedom of information show that only 20 per cent of those cameras are active and ready to snap speeding drivers at any given time. That represents a drop from the one in three cameras working in 2011.
Road safety campaigners said the figures were disappointing -but safety camera bosses insisted the deterrence effect remained even if cameras were not always working.
Ed Morrow, campaigns officer for road safety charity Brake, said: "It is disappointing that safety camera partnerships in Scotland are not making full use of the resources available to stop speeding drivers putting lives at risk.
"Brake fully supports the use of speed cameras, which are proven to cut speeds and save lives.
"We need higher fines and more dedicated traffic police on the ground to deter speeding and other risky driving behaviour, but we also need all drivers to take personal responsibility for their actions and stick to the limit."
Scotland's eight safety camera partnerships were asked to disclose how many fixed roadside speed cameras they operate - and how many were working for a full week in June.
Four of the eight authorities - North East, Lothian and Borders, Strathclyde and Tayside - operate fixed cameras, while the rest - Central Scotland, Dumfries and Galloway, Fife and Northern - run only mobile camera vans.
The North East Safety Camera Partnership said that they have 25 safety camera sites - but only five were running during the period.
Of the Strathclyde partnership's 63 cameras only 15 were operational - while only three of Tayside's 14 fixed camera sites were active. Meanwhile, the Lothian and Borders partnership said they run 67 fixed camera sites, but just 11 of the 67 were active daily during the week.
Neil Macgilivray, spokesman for Scotland's safety camera partnerships, said the deterrence effect was maintained as drivers can't tell if cameras are live or not.
He added: "Numbers of active cameras are slightly lower than usual at the moment as safety camera partnerships are in the process of converting film cameras to digital technology.
"This work should be completed within the next month."