13 July 2017

Speed cameras to reduce speeding traffic and road traffic injuries

This review on the use of speed cameras was conducted by Dr Phil Edwards and Dr Chloe Perkins of the London School of Hygiene and Tropical Medicine.

What is the systematic review about?

The aim of this review was to provide an update of the Cochrane systematic review of traffic speed enforcement cameras, and to explore under which circumstances speed cameras may, or may not work, and to assess whether any effects differ by type of device (i.e. covert versus overt, fixed versus mobile cameras). The evidence is taken from a review covering 51 studies, which was sufficiently systematic that most forms of bias that could influence the study conclusions could be ruled out. 

This review provides evidence that speed cameras are an effective intervention for reducing speeding behaviour, and can help combat some of the negative consequences of speeding such as fatalities and injury collisions. Considering continuing increases in traffic volumes, speed cameras appear to be a worthwhile intervention to protect public safety.

What does it tell us about the impact of speed cameras?

The evidence evaluated in this updated review shows speed cameras bring about consistent reductions in both speed and collision outcomes. Results suggest that the implementation of speed camera programmes is associated with a:

  • 7% reduction in average speed
  • 52% reduction of vehicles exceeding the speed limit
  • 19% reduction in collisions
  • 18% reduction in collisions resulting in injuries
  • 21% reduction in severe or fatal collisions.

There was no evidence that the effect of speed cameras differed by whether the camera was overt or covert. However, there was some evidence to suggest that fixed cameras had a slightly greater effect on all road traffic collisions and those resulting in fatalities or severe injuries, than mobile cameras.

How do speed cameras make an impact?

The literature reviewed considered speed cameras to work through deterrence, specific and general. Specific deterrence focuses primarily on apprehending and punishing the individual offender, and assumes that once caught and brought to justice, they will consequently avoid re-offending. General deterrence focuses on the wider population and assumes the threat of punishment will deter people from, in this case, speeding through a desire to avoid legal consequence. The greater the perception of risk of punishment, the greater the likelihood that general deterrence will be effective.  

In which contexts do they work best?

There are likely to be a number of pre-existing conditions that may influence the effectiveness of speed cameras, these could include factors such as road type, speed limits, setting (urban or rural) and weather. Primary studies only provided enough information to empirically test one of these, the influence of rural and urban areas, and the effect of speed cameras was not found to differ between these area types.  

How do you implement them to get the best impact?

The implementation of speed cameras can differ in a number of ways, such as whether they are obviously visible (covert or overt systems), mobile or fixed and their level of enforcement (operational hours and penalties issued). The review did not find evidence that the effects of speed cameras differed if they were used covertly or overtly but found some evidence to suggest that fixed cameras had a greater effect on all road traffic crashes and those resulting in fatalities or severe injuries, than mobile cameras.

What do they cost?

All of the primary studies that reported economic analyses conveyed positive outcomes, although their details were not comparable and so could not be synthesised in the review.  One primary study evaluating 56 mobile safety cameras in the UK Northumbria Police area estimated that around £30,000 was saved in treatment costs (from casualties prevented) alone, over the two years of the study. Cost-benefit ratios estimated that the benefits exceed the estimated costs of speed camera programmes by at least 3:1, and were larger when the time horizons were five years or more. 

This review is the eighth in the What Works: Crime Reduction Systematic Review Series.

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