Red-light cameras (RLCs) are an enforcement mechanism that permit the remote enforcement of traffic signals to prevent crashes occurring after running a red light.
RLCs are a fully automated photo detection system that includes three key elements: cameras, sensors or triggers, and a computer. The cameras may take still or video images, or both; modern systems generally use digital cameras but some older systems may use 35-mm wet film cameras. In the UK, the cameras are usually placed on one arm of an intersection where a red light running problem has been identified. In the USA the cameras generally are located on all four corners of an intersection, so that vehicles coming from any direction may be photographed from multiple angles.
The cameras are activated when a vehicle moves over the triggers at a predetermined speed. After the RLCs have captured images of the violation, the evidence is reviewed and penalty tickets sent to the address where the violating vehicle is registered.
The focus of this review is on the prevention of red light running (RLR), road traffic crashes, and injuries and fatalities resulting from road traffic crashes. This narrative is based on one updated meta-analytic review covering 38 studies (28 of which were new since the last review) and including a total of 41 separate analyses. 26 of the primary studies in the review were based on evidence from the USA, 8 from Australia, 2 from Canada and 2 from Singapore.
Overall, the evidence suggests that the intervention has reduced red light violations.
The meta-analysis found that RLC programmes led to reductions in: red light violations (-61%), right angle crashes (-24%), right angle injury crashes (-29%), and in total injury crashes (-20%) Conversely, RLCs were also associated with an increase in rear-end crashes (+19%).
The review was sufficiently systematic that most forms of bias that could influence the study conclusions can be ruled out.
The evidence is taken from a systematic review covering 38 studies, which demonstrated a high-quality design in terms of having a transparent, and well-designed search strategy, featuring a valid statistical analysis, sufficiently assessing the risk of bias in the analysis and giving due consideration to the way outcomes were measured and combined. The review did not explore the issue of publication bias.
The review suggests that the primary mechanism by which RLCs reduce RLR is deterrence, although no mechanisms were specifically tested in the studies. This involves the threat of being caught and punished discouraging people from offending and may operate in the following ways:
RLCs are designed to increase the actual risk of apprehension as well as the perceived risk of apprehension, to create a general deterrent effect. The impact of RLCs may not be limited to only those junctions with cameras, they may also create a diffusion of benefit, so that they have a more general effect on driver behaviour on the roads.
The review notes that the effect of the intervention might differ by time and day of week, signal timing, or average daily traffic but there was not enough information in the primary studies to analyse these potential moderators. The review did examine whether the effect of RLCs differed by country (USA and Australia) but found few differences in the effect of RLCs on most outcomes.
The review identifies a number of implementation issues. First, public knowledge of the implementation of an RLC programme is considered essential for success. Many of the programmes that were tested included publicity campaigns and warning signs to increase driver awareness of the RLCs in order to enhance their deterrent effect. This review explored the effect of warning signs on total crashes and total injury crashes in primary studies but found no significant difference in the effect of RLCs on either outcome.
Other implementation issues identified in the report include:
Many of the studies did not include any economic information; those that did varied widely in the amount of detail provided. None of the studies conducted a full cost-benefit analysis that included both economic viability and societal benefits (including crash costs). While studies examining economic viability in the USA and Australia found mixed results, an early cost benefit analysis in the UK identified significant benefits for RLCs with most areas able to obtain a net benefit within one year.
Overall, the evidence suggests that RLC programmes led to reductions in red light violations, right angle crashes, right angle injury crashes and total injury crashes. However importantly, RLCs were also associated with an increase in rear-end crashes. Primarily, RLCs are thought to reduce RLR through deterrence. A number of potential moderators were identified such as time and day of week, signal timing, or average daily traffic but were not tested in the studies. While public knowledge of RLCs is considered important for the success of the intervention, this review found no evidence that warning signs were associated with a change in the effect of RLCs on total crashes and total injury crashes. Further studies are need to examine economic considerations around RLCs.
Perkins, C., Steinbach, R., Edwards, P., Beecher, D., Hess, S., Aeron-Thomas, A., Cohn, E., Kakar, S. (2017) Red light enforcement cameras to reduce traffic violations and road traffic injuriesThis narrative was prepared by the Cochrane Injuries Group in the Faculty of Epidemiology and Population Health at the London School of Hygiene and Tropical Medicine and was co-funded by the College of Policing and the Economic and Social Research Council (ESRC). ESRC Grant title: 'University Consortium for Evidence-Based Crime Reduction'. Grant Ref: ES/L007223/1.Uploaded 20/02/2018