Fatal flaw in PSNI claims says Safe Speed
Safe Speed Press information

 release date: 9th June 2004 number: PR125 (Northern Ireland only)

Fatal flaw in PSNI claims says Safe Speed

News. For immediate release.

Recently the Police Service of Northern Ireland claimed that there had been a 27 per cent drop in killed and seriously injured persons "at speed camera sites". Such claims have been made across Britain, and we don't doubt that there was such a reduction. But were the cameras responsible or is it just a statistical quirk?

Paul Smith, founder of the Safe Speed road safety campaign said: "It's frightening that the Police are again abusing statistics in this way. The benefit that they are claiming for their cameras is actually well known to
statisticians as a "regression to the mean benefit illusion". Paul explains: "Suppose we had a 50 injury accident on a motorway. If they placed a camera at the site, next year they would claim that 50 injuries had been saved by the camera. Of course the mistake is that when a camera is placed at the site of a random cluster of accidents we would expect accidents to go down. Unless they properly compensate for this effect, their figures are meaningless."

Paul continues: "The UK government is also guilty of the same statistical abuse. In the report of the two year pilot scheme for speed camera hypothecation they claimed there was a 35% reduction in killed and seriously
injured" at speed camera sites. We estimate the regression to the mean benefit illusion at 50%, which means that it's very possible that the cameras actually made the roads more dangerous. After correspondence we eventually got the authors of the report to admit their error on radio 4."


Notes for editors:


Correspondence with the main author of the DfT report:

Interview on Radio 4:

Radio 4 audio recording:
http://www.safespeed.org.uk/moreorless.mp3 (4.5MB)

Regression to the mean explained in more detail:

new: Heydecker does it again:
http://www.safespeed.org.uk/pr126.html and

About Safe Speed

Since setting up Safe Speed in 2001, Paul Smith, 49, an advanced motorist and road safety enthusiast, and a professional engineer of 25 years UK experience, has carried out about 5,000 hours of research into the overall effects of speed camera policy on UK road safety. We believe that this is more work in more detail than anything carried out by any other organisation. Paul's surprising conclusion is that overall speed cameras make our roads more dangerous. Paul has identified and reported a number of major flaws and false assumptions in the claims made for speed cameras, and the whole "speed kills" system of road safety.     

The inescapable conclusion is that we should urgently return to the excellent road safety policies that gave us in the UK the safest roads in the World in the first place.     

Safe Speed does not campaign against speed limits or appropriate enforcement of motoring laws, but argues vigorously that automated speed enforcement is neither safe nor appropriate.     

Contact Safe Speed:     

web: http://www.safespeed.org.uk     
email : psmith@safespeed.org.uk    
telephone: 01862 832000 anytime.     
mobile: 07799 045553 note: the mobile does not work well at our office. Always try land line first.     
Location: North Scotland     

We are available for press and media interviews.

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Created 22/06/2004. Last update 22/06/2004