34,351 people were killed or seriously injured on the roads of Great Britain in 2004, including 3,905 children (1), with those from lower socioeconomic groups being disproportionately affected (2). Predictions show that this level of accidents will increase dramatically over coming years (3), and so the tackling of this issue should be a public health priority. However, in reality, the prevention of road crashes is low on the agenda, with little research and development being undertaken in this area (4).

The Department for Transport states that speed is the single biggest contributory factor to road casualties (5). One response is to install road safety cameras, designed to allow the prosecution of those exceeding speed limits, and to deter others from speeding. Yet, since their introduction in the UK in 1991 (6), speed cameras have proved consistently controversial, with some groups claiming that safety cameras increase accident rates (7), and others claiming that speed per se has no impact on the likelihood of being involved in a road traffic accident (8). Having reviewed the evidence, however, I am confident that speed cameras improve road safety, and so should be a public health priority.

Research has been undertaken into the effect of drivers’ speed on the frequency of road accidents (9). This provides strong evidence based on very extensive data that as speed increases, so the likelihood of crashing also increases (Fig 1). A number of hypotheses as to why this relationship exists are put forward, including the notion that higher speeds give drivers less time to react appropriately to sudden changes in driving conditions. Whilst some try to counter the research by stating that there are fewer accidents on motorways than other roads, and these are the roads where people drive fastest (10), the TRL research studies changes in risk in relation to speed limit, rather than changes according to raw speed, making the argument irrelevant.

It is also noted that increased speed increases crash injury. For example, the likelihood of death for passengers in a car crashing at 50 miles per hour is twenty times greater than that for a car crashing at 20 miles per hour (11). Figure 2 shows a similar relationship for impacts with pedestrians.

It is clear, therefore, that if speed cameras reduce the speed of cars on the road, particularly in areas where accident rates are high, safety will be increased, and hence health protected.

There is some evidence, however, that speed cameras are not effective in reducing accident rates. Keenan (12) recognises that whilst the majority of speed cameras operate at only one point, the problem of speeding generally causes a problem over a stretch of road. Where single-camera systems are used, he provides evidence that people slow down for the camera itself, and then speed up again. His recommendation is that series of linked cameras should be used, so that an average speed over a greater distance can be measured. Where this method has been put into operation, speed reduction for the entire length of the dangerous stretch of road has been more successful.

Arguments about unfairness in speed camera prosecutions, leading to apparently “safe” drivers being caught while “dangerous” ones get away (13) can largely be refuted by evidence which shows (14) that those caught by a speed camera had twice the chance of being involved in a recent crash over the general population, as well as the bare fact that only those caught actually breaking the law are prosecuted.

A systematic review of 14 studies related to speed cameras (15) concluded that “speed cameras are an effective intervention in reducing road traffic accidents”. It is clear, however, that few of the included studies had valid control groups, and so some of the evidence is potentially questionable. The evidence was so strong, however, that it is fair to say that the evidence that speed cameras reduce accidents is clear.

Taking the evidence as a whole, it is clear that traffic accidents are a major public health issue, and that speed cameras can help tackle this. There is clearly a need for further surveillance, assessment, collaborative work in the area to assess best practice for speed camera types and locations. More independent research in the area would be welcomed, as much evidence is potentially biased due to being undertaken by action groups. However, it is clear that speed cameras reduce mortality and morbidity in the population, have the potential to increase health equality, and a growing evidence base. It would appear, therefore, that they are indeed an appropriate health protection intervention.

References

1. Department for Transport. Road Casualties Great Britain: 2004 Annual Report. The Stationery Office, 2005. p6
2. Laflamme L, Diderichsen F. Social differences in traffic injury risks in childhood and youth – a literature review and a research agenda. Injury Prevention 2000; 6:293-298
3. Penden M, et al. World report on road traffic injury prevention. World Health Organisation, 2004. p3
4. Roberts I, et al. War on the Roads. BMJ 2002;324(7346):1107
5. Department for Transport. Tomorrow’s Roads: Safer for Everyone. The Stationery Office, 2000. p37
6. Corbett C, Simon F. The effects of speed cameras: How drivers respond. Brunel University Centre for Criminal Research, 1999. p1
7. Parliamentary Advisory Council on Transport Safety. Speed Cameras: Ten criticisms and why they are flawed. PACTS, 2003. p1
8. Association of British Drivers. The Truth about Speed. http://www.abd.org.uk/speed_truth.htm [accessed 22rd January 2006]
9. Taylor M, et al. The Effects of Drivers’ Speed on the Frequency of Road Accidents. TRL Report 421, 2000.
10. SafeSpeed. TRL421 and TRL511: Propaganda or Science. http://www.safespeed.org.uk/trl421.html [accessed 22nd January 2006]
11. Penden M, et al. op. cit., pp77-78
12. Keenan D. Speed Cameras: How do drivers respond? Traffic Engineering and Control 2004; 45(3):104-111
13. RAC Foundation. Profile of a Speeder. http://www.racfoundation.org/releases/031103rac.htm [accessed 22nd January 2006]
14. Stradling S, et al. The Speeding Driver: Who, how and why? Scottish Executive Social Research Findings 170/2003
15. Pilkington P, Kinra S. Effectiveness of speed cameras in preventing road traffic collisions and related casualties: systematic review. BMJ 2005; 330:331-334