Speed cameras: what does the evidence say?

Welcome to another in my occasional series on useful, interesting or controversial findings from academic studies. Today’s it is the question of speed cameras, for which a study of international evidence has recently been conducted:

To evaluate the effectiveness of speed cameras, the authors examined all eligible studies, that is, studies that met pre-set standard criteria. We analysed the effect of speed cameras on speeding, road traffic crashes, injuries and deaths by comparing what was happening in road areas before the introduction of speed cameras and after their introduction, and also by analysing what was happening in comparable road areas where no speed cameras were introduced during the study period.

The authors accepted a total of 35 studies for review which met the pre-set criteria. All studies reporting speed outcomes reported a reduction in average speeds post intervention with speed cameras. Speed was also reported as either reductions in the percentage of speeding vehicles (drivers), as percentage speeding reductions over various speed limits, or as reductions in percentages of top end speeders. A reduction in the proportion of speeding vehicles (drivers) over the accepted posted speed limit, ranged from 8% to 70% with most countries reporting reductions in the 10 to 35% range.

Speed cameraTwenty eight studies measured the effect on crashes. All 28 studies found a lower number of crashes in the speed camera areas after implementation of the program. In the vicinity of camera sites, the reductions ranged from 8% to 49% for all crashes, with reductions for most studies in the 14% to 25% range. For injury crashes the decrease ranged between 8% to 50% and for crashes resulting in fatalities or serious injuries the reductions were in the range of 11% to 44%. Effects over wider areas showed reductions for all crashes ranging from 9% to 35%, with most studies reporting reductions in the 11% to to 27% range. For crashes resulting in death or serious injury reductions ranged from 17% to 58%, with most studies reporting this result in the 30% to 40% reduction range. The studies of longer duration showed that these positive trends were either maintained or improved with time.

The quality of the included studies in this review was judged as being of overall moderate quality at best, however, the consistency of reported positive reductions in speed and crash results across all studies show that speed cameras are a worthwhile intervention for reducing the number of road traffic injuries and deaths.

To affirm this finding, higher quality studies, using well designed controlled trials where possible, and studies conducted over adequate length of time (including lengthy follow-up periods) with sufficient data collection points, both before and after the implementation of speed cameras, are needed.

Speed Camera Impact

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12 Comments

  • Nonconformistradical 20th Oct '10 - 10:43am

    Report can be downloaded at http://onlinelibrary.wiley.com/o/cochrane/clsysrev/articles/CD004607/pdf_fs.html without going via s–dd–g b—-y facebook

  • Very poor analysis of the effects of Regression To The Mean.

    Put a hidden flag up and the rate of accidents will be lower in future months from whatever peak accident the flag started from.

  • Nonconformistradical 20th Oct '10 - 12:00pm

    “There’s a download button at the top of the embedded report – that gives a pdf download”

    Tried it – It takes one to Facebook!!!!!!!!!

  • coldcomfort 21st Oct '10 - 9:51am

    The flaw in every analysis of the effects of speed limit enforcement on accidents, especially the severity of accidents, is the unquestioned assumption that any given speed limit is sensible & rational. But it clearly is not. Any driver knows of roads where 40mph is perfectly safe on grounds of visibility, road width, distance of houses from the road, likelihood of child running unseen into the road and so on & so on yet there is a 30mph limit based on no science or logic & usually carrying a camera because it makes money & conversely roads where 30mph is downright dangerous yet legal & usually do not have a camera. Also the statistics do not usually distinguish between a collision where vehicles are doing less 20% above this arbitrary limit ( 36mph in a 30 limit) and those that are going seriously fast. If speed limits were sensible, reflected real road conditions & the technical capability of modern cars they would be obeyed because that’s how the vast majority of drivers drive. When the speed limit of 30mph was introduced in 1934 most vehicles could only manage 65mph max. & braking distances were at least twice what they are now.

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