Speed cameras cut injuries by a quarter - RAC research
Speed cameras cut the number of serious injuries in road accidents in the areas where they are placed by an average of more than a quarter, a study suggests.
The research by the RAC Foundation was based on data from 551 fixed camera sites in nine areas of England.
Twenty-one sites bucked that trend, however, with the number of injuries going up.
The RAC Foundation said the findings showed how effective speed cameras were for road safety.
The study found that after cameras were installed the average number of fatal or serious injuries fell by 27%.
The authors of the report have written to those councils where the figures have risen suggesting that they try to find out why this is the case.
RAC Foundation director Stephen Glaister said: "Safety cameras are contentious, people dispute whether they work.
"But in fact the general public as a whole like them because they want these roads to be made safer.
"If cameras were turned off overnight there would be something like 80 people killed extra a year and 800 people killed or seriously injured.
"So the evidence is very good that on average they do work, they are effective."
Speaking later on BBC Radio 4's Today programme, Mr Glaister also said that speed cameras represented "very good value for money".
But Claire Armstrong, the co-founder of campaign group Safe Speed, disputed his conclusions, arguing that speed was a factor in just 6% of road accidents.
"Speed cameras have unintended consequences and have given rise to some collisions and casualties that would not have occurred if the cameras had not been deployed," she said.
The main cause of road accidents was driver concentration, she suggested, so reducing speed was not a "panacea".
"If you are simply driving at, let's say, 20mph you are not necessarily concentrating... and if you're not concentrating and paying attention to the road ahead, and you therefore cannot stop in the distance you know to be clear in, it doesn't matter what speed you are doing, you potentially will still have an accident.
"We know there are accidents that will kill you at 3mph and accidents where you will not die at 80mph."
The coalition cut Whitehall funding for speed cameras when it came to power.
It said police and local councils relied on the devices too much, and should use a range of different methods to improve road safety.
But a study last year suggested that so far most councils had kept speed cameras in place.
BBC transport correspondent Richard Westcott said speed cameras have been controversial since they were introduced 20 years ago - but this research suggests most of them make roads safer.