The media reportage on the effects of the decommissioning of speed cameras on road traffic accidents in Swindon has already caused Full Fact some concern today.

However the factual problems in this debate do not begin and end in the Wiltshire town.

With Oxfordshire announcing last week that it would follow Swindon’s lead in switching off their under-fire cameras and the Government cutting maintenance funding for those still in use, the Taxpayers’ Alliance released a report questioning their impact on road safety.

This suggested that the decline in accidents on Britain’s roads actually slowed after the introduction of speed cameras in 1992.

This analysis uses Department for Transport (DfT) Reported Road Accidents and Casualties data to trace the impact of speed cameras on road traffic accidents nationwide.

Richard Littlejohn, writing in this morning’s Daily Mail, uses these findings to argue that the use of speed cameras has resulted in “ever-diminishing returns in road safety”.

But do these conclusions stand up to closer analysis? Some road safety campaigners suspect not.

The first cracks in the argument began to emerge when Full Fact probed the source of the data. As a DfT spokesperson told us, departmental road accident statistics aren’t necessarily the best basis for gauging the success or failure of speed cameras.

“When you consider the range of factors that have contributed to the long-term improvement in road safety, from social changes to drink driving legislation, it is difficult to draw any useful conclusions with any confidence on speed cameras,” he said.

Furthermore he pointed out that it “would be much more useful to look at the number of accidents recorded at camera sites.”

Just such an analysis was indeed undertaken in 2005 by researchers at University College London (UCL). They found that accidents were down 22 per cent over the four years 2000-4 at sites where speed cameras were introduced, with the number of those killed or seriously injured falling 32 per cent over the same period at these sites.

Unlike the Taxpayers’ Alliance analysis, the UCL report also accounts for long-term trends in their calculations, making it a more reliable measure of the impact that is directly attributable to speed cameras.

This was achieved by calculating the ‘regression to mean’ – a statistical technique used to analyse the rate of change in any long-term trend. As the report notes: “Whilst regression-to-mean does appear to account for some of the reduction in collisions at cameras, the safety effects of cameras remain substantial.”

As with Swindon, the terms of reference for the national debate on the efficacy of speed cameras do seem to have focused on information that does not necessarily give a full reflection of the breadth of opinion on the matter.

Whilst the UCL report is now five years old, it does represent a more nuanced analysis than that offered by the Taxpayers’ Alliance, and such findings should be considered in media reporting of the subject if we are to achieve a balanced debate.