Citation

Mountain L, Hirst W, Maher M. Traffic Eng. Control 2004; 45(8): 280-287.

Affiliation

Department of Civil Engineering, University of Liverpool, Liverpool L69 3GQ, United Kingdom

Copyright

(Copyright © 2004, Hemming Group)

DOI

unavailable

PMID

unavailable

Abstract

The effect of speed enforcement cameras on accidents continues to be a source of considerable controversy. Recent headlines claim that they save around 100 lives a year in the UK while opponents still argue that they are a distraction to drivers and as a consequence may actually increase the road death toll. This paper presents a detailed evaluation of the impact of 62 fixed cameras on 30mph roads in the UK. The changes in accident frequency attributable to the effect of cameras on both speed and route choice are separately estimated, as are the changes due to general trends in accidents and regression-to-mean: changes that would have occurred with or without a camera. It was found that the average effect of the cameras was a fall in personal injury accidents of some 25%, of which a fall of some 20% was attributable to their impact on speed with a 5% fall due to diversion of traffic away from routes with cameras. Safety improvements were observed over a distance of up to 1km upstream and downstream of the cameras, with no evidence that any sudden changes in speed on approaching or passing the cameras had any detrimental effect on safety. The impact of the cameras on fatal and serious accidents was rather less certain and served to highlight the dangers of ignoring regression-to-mean effects. while reductions of the order of one third were observed, more than half of this was attributable to regression-to-mean. It is argued that the current guidelines for locating cameras, and the criteria for judging their success or failure, place too much emphasis on observed numbers of fatal and serious accidents without proper controls for regression-to-mean some roads which might benefit from increased speed enforcement may not qualify for a camera while cameras which are actually improving road safety may be judged unsuccessful.