No evidence speed cameras raise crash risk

"Speed cameras 'increase risk of serious or fatal crashes','' the Daily Mail tells us, while The Guardian, covering the same report, says "Speed cameras reduce serious road accidents." So you could be forgiven for being more than a little confused.

So what is the picture – do they increase or decrease injuries and fatal crashes?

The main objective of the report published last month by the RAC Foundation was to provide guidance on how speed camera data (which has been publicly available since 2011) should be analysed and interpreted. And not, despite the media’s take on the report, to provide simple figures on the number of collisions and fatalities in the vicinity of each camera.

For this reason, the report mostly consists of detailed discussion into statistical analysis and not real-world outcomes. Though it did provide some data for nine local authorities and road safety partnerships.

The figures for the nine regions reviewed present somewhat mixed results.

Five of the regions showed significant decreases both in the number of fatal or serious collisions (FSCs – decreases ranging from 24–53%), and collisions resulting in personal injury of any severity (PICs – decreases ranging from 20-32%) following introduction of cameras.

However, four of the regions did not find the introduction of cameras to have had a significant effect on FSCs and PICs.

Based on the data provided for the regions studied, we can only conclude that speed cameras have helped to reduce the number of collisions resulting in fatality or injury in some areas. But that in other areas they have had no significant effect.

However, no evidence is presented here to suggest they increase the risk of fatality or injury as was reported in some sections of the UK media.

Who produced the report and what evidence did it look at?

The report, published last month, titled "Guidance on the use of speed camera transparency data" was conducted by the Royal Automobile Club (RAC) Foundation and authored by Richard Allsop, Professor of Transport Studies, of University College London.

The RAC Foundation is a charity focusing on road safety and transport issues.

The report says that since Summer 2011, data relating to fixed speed cameras has been made available to the public and is presented on the websites of local authorities or road safety partnerships. A list of these websites can be found through on the Department for Transport.

Available data contains information for the period 1990 to 2010 on the number of collisions and casualties near each camera, typically on a 0.4 km to 1.5 km section of road. The RAC have used this information to find, for each camera, the year by year numbers of:

• fatal or serious collisions (FSC)
• number of people killed or seriously injured (KSI) in the FSCs
• collisions resulting in personal injury of any severity (PIC)
• number of casualties of all severity (CAS) in the PIC

Information is also available from websites regarding:

• observations of the speed of traffic near the camera on certain dates
• the numbers of offences detected by the cameras and actions taken in respect of the offenders

However, these things were not the focus of this report.

The RAC Foundation considered that the general public needed guidance on how to interpret this data, and this was the focus of the report. The Foundation downloaded data from nine local authorities and road safety partnerships and conducted statistical analysis before submitting their findings for independent peer review. The nine areas covered a mix of metropolitan and shire counties, including Warwickshire, Lincolnshire, Merseyside and Sussex.

The focus of this report was to "discuss a number of ways in which the data can be analysed, and provide users of the data [with] practical advice on the scope and nature of the available data and on their analysis and interpretation". It was not, as the media implied, to produce simple figures on collision and fatality rates.

The hope is that once an agreed method of analysis is reached, simple figures on collision and fatality rates, will be made available.

What were the main findings of the report?

The report initially raises several practical difficulties of examining the data:

• asking holders of data to make them available in a recommended form does not necessarily result in the data being made available in that form or at all
• websites and their addresses often change, so any central source of such addresses needs to be robust with respect to such changes
• users will want to work with data, not just read information on a screen or printout, so data should be mounted in a format that enables use with minimum transcription, that is in a spreadsheet or analogous format
• while users should of course be free to make their own analyses and interpretations of data that is made available, this can be helped by objective and non-directive advice about the nature and characteristics of the data concerned and pointers towards available techniques that are appropriate for application to data of that kind

The focus of their report is a fairly complex discussion of how to statistically interpret the data and look at how number of collisions in the vicinity of one camera relates to those in the whole partnership areas, and how numbers of FSC, KSI, PIC and CAS relate to each other.

Since the media focus is on changes in the numbers of collisions and fatalities, below is some of the data presented in appendices.

The following regions demonstrate significant decreases in PICs and FSCs since camera establishment:

• 24 cameras in Warwickshire showed a 25% decrease in the number of PICs and 38% decrease in the numbers of FSC in the vicinity of cameras since their establishment. In the three years prior to cameras in this area, PICs had been rising by 14% and FSCs rising by 57%
• 15 cameras in Leicester, Leicestershire and Rutland showed a 28% decrease in the number of PICs and a 53% decrease in FSCs since camera establishment. In the three years prior to cameras in this area, PICs had been rising by 14% and FSCs decreasing by 1%
• 42 cameras in Staffordshire and Stoke on Trent (an area of fewer crashes) showed a 32% decrease in the number of PICs and 44% decrease in FSCs since camera establishment. In the three years prior to cameras in this area PICs had been decreasing by 3% and FSCs decreasing by 1%
• 26 cameras in Staffordshire and Stoke on Trent (an area of more crashes) showed a 23% decrease in the number of PICs and 29% decrease in FSCs since camera establishment. In the three years prior to cameras in this area PICs had been decreasing by 13% and FSCs decreasing by 29%
• 55 cameras in Sussex showed a 21% decrease in the number of PICs and 36% decrease in FSCs since camera establishment. In the three years prior to cameras in this area, PICs had been increasing by 11% and FSCs increasing by 30%
• 203 cameras in Thames Valley showed a 20% decrease in the number of PICs and 24% decrease in FSCs since camera establishment. In the three years prior to cameras in this area PICs had been increasing by 3% and FSCs decreasing by 2%

Three of the remaining regions showed non-significant changes:

• 47 cameras in Cambridgeshire and Peterborough showed a 1% increase in the number of PICs since camera establishment (though a 42% drop in FSCs)
• 50 cameras in Lincolnshire showed a 9% decrease in the number of PICs and 15% decrease in FSCs since camera establishment
• 33 cameras in Merseyside showed an 11% increase in the number of PICs and 5% increase in FSCs since camera establishment
• 56 cameras in South Yorkshire showed a 1% increase in the number of PICs and 16% decrease in FSCs since camera establishment

How accurate was the media coverage?

In general, the media's coverage of this report was rather confusing and contradictory.

It appears the media wanted to report on the extent to which speed cameras decrease – or increase – the number road collisions and fatalities.

However, this wasn’t the objective of this report, which was a lot more complex, and focused on guiding people in how to interpret available data on speed cameras. 

The Daily Mail’s coverage of the report was particularly poor and arguably disingenuous. The claim that “Speed cameras increase the risk of serious or fatal accidents” is simply not backed up by the data.

The Mail seems to be resorting to what, in academic circles, is known as cherry picking – that is, focusing on the data that supports your argument while ignoring the data that doesn’t.

It was the case that at 21 camera sites the number of accidents went up – though whether this was due to speed cameras remains unproven. Leaving that issue aside, the Mail ignores any data from the remaining 530 camera sites where the number of accidents and fatalities went down.

Such a distortion of evidence is disturbing.

Based on the data provided for the regions studied here we can only conclude that speed cameras have helped to reduce the number of collisions resulting in fatality or injury – or that in some areas they have had no effect. However, no evidence is presented here to suggest that they increase them.