New research suggests road deaths could be cut by more than two-thirds in areas around speed cameras.
Studies examined the effects of fixed roadside cameras
Researchers from Bristol's two universities reviewed 14 studies and found wide variations.
The report, which drew together research from around the world, found that cameras appeared to cut collisions, deaths and injuries.
But the Association of British Drivers (ABD) dismissed the findings as pro-speed camera "propaganda".
The report from the University of Bristol and the University of the West of England (UWE) found that figures varied radically, with the impact of cameras on death rates ranging from a reduction of 71%, to a more modest 17%.
Equally, collisions were cut by between 5% and 69%, while injuries fell between 12% and 65%.
Author Paul Pilkington, public health lecturer at UWE, said: "Speed cameras have an effect but there are other factors such as traffic volumes and other traffic calming measures, it's about being able to unpick the factors."
While some of the studies examined the effects of fixed roadside cameras located at blackspots, others looked at mobile mounted devices.
Despite the variety of studies involved, the researchers say they were unable to find an overall pattern on which method was most effective.
"We need to know exactly how cameras are best used," Mr Pilkington said.
ABD spokesman Nigel Humphries claimed the increase in speed cameras on British roads had not reduced the total number of road deaths.
"Because cameras are unpopular, their fans produce a constant barrage of propaganda to try and justify them," he said.