Average speed cameras now cover more than 250 miles of road in the UK, new research has found.
According to the RAC Foundation, more than 50 sections of road are now permanently managed by the cameras, equating to 256 miles under observation.
These figures do not take into account cameras used on a temporary basis, for example when used to manage traffic through roadworks.
The organisation claimed the length of UK roads covered by average speed cameras has more than doubled since 2013.
The sections being monitored range in length from a quarter of a mile over Tower Bridge to 99 miles on the A9 in Scotland.
"Average speed cameras are becoming a more common fixture on Britain's roads," said Steve Gooding, director of the RAC Foundation. "Unsurprisingly, the indications are that compliance with the speed limit through stretches of road managed by average speed cameras is high, but the acid test is whether accident and casualty rates have also fallen."
"Rightly or wrongly many motorists perceive the current 'spot' speed cameras to be more about raising revenue for the Treasury than saving lives, but average speed cameras have greater potential to bring drivers on side," he added.
The group added it will now assess the effectiveness in reducing the number of accidents by compared pre-installation data with post-installation stats.