Speed cameras for the prevention of road traffic injuries and deaths: Cochrane systematic review
Assessed as up to date: 2010/05/03
It is estimated that by 2020, road traffic crashes will have moved from ninth to third in the world ranking of burden of disease, as measured in disability adjusted life years. The prevention of road traffic injuries is of global public health importance. Measures aimed at reducing traffic speed are considered essential to preventing road injuries; the use of speed cameras is one such measure.Objectives
To assess whether the use of speed cameras reduces the incidence of speeding, road traffic crashes, injuries and deaths.Search methods
We searched the following electronic databases covering all available years up to May 2010: the Cochrane Library, MEDLINE (WebSPIRS), EMBASE (WebSPIRS), TRANSPORT, IRRD (International Road Research Documentation), TRANSDOC (European Conference of Ministers of Transport databases), Web of Science (Science and Social Science Citation Index), PsycINFO, CINAHL, EconLit, WHO database, Sociological Abstracts, Dissertation Abstracts, Index to Theses.Selection criteria
Randomised controlled trials, interrupted time series and controlled before-after studies that assessed the impact of speed cameras on speeding, road crashes, crashes causing injury and fatalities were eligible for inclusion.Data collection and analysis
We independently screened studies for inclusion, extracted data, assessed methodological quality, reported study authors' outcomes and where possible, calculated standardised results based on the information available in each study. Due to considerable heterogeneity between and within included studies, a meta-analysis was not appropriate.Main results
Thirty five studies met the inclusion criteria. Compared with controls, the relative reduction in average speed ranged from 1% to 15% and the reduction in proportion of vehicles speeding ranged from 14% to 65%. In the vicinity of camera sites, the pre/post reductions ranged from 8% to 49% for all crashes and 11% to 44% for fatal and serious injury crashes. Compared with controls, the relative improvement in pre/post injury crash proportions ranged from 8% to 50%.Authors' conclusions
Despite the methodological limitations and the variability in degree of signal to noise effect, the consistency of reported reductions in speed and crash outcomes across all studies show that speed cameras are a worthwhile intervention for reducing the number of road traffic injuries and deaths. However, whilst the the evidence base clearly demonstrates a positive direction in the effect, an overall magnitude of this effect is currently not deducible due to heterogeneity and lack of methodological rigour. More studies of a scientifically rigorous and homogenous nature are necessary, to provide the answer to the magnitude of effect.
Wilson Cecilia, Willis Charlene, Hendrikz Joan K, Le Brocque Robyne, Bellamy Nicholas
Do speed cameras reduce road traffic crashes, injuries and deaths?
Road traffic crashes are a major cause of death and disability. The speed at which a vehicle travels is an important determinant of injury; the faster the vehicle is travelling, the greater the energy inflicted on the occupants during a crash, and the greater the injury.
Excessive speed (driving faster than the posted limit or too fast for the prevailing conditions) has been found to contribute to a substantial number of crashes. It is predicted that, if the number of speeding drivers is reduced, both the likelihood and severity of a crash will be lowered. Therefore, interventions aimed at reducing traffic speed are considered essential to preventing road injuries and deaths. The enforcement of safe speeds with speed cameras and associated automated devices is one such measure.
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.
Twenty 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. As none of the studies were conducted in low-income countries, research in such settings is also required. There is a greater need for consistency in methods, such as international standards for the collection and reporting of speed and crash data and agreed methods for controlling bias in studies. This would allow more reliable study comparisons across countries, and therefore greater ability to provide stronger scientific evidence for the beneficial effects of speed cameras.
Implications for practice
Speed cameras and related automated enforcement devices are worthwhile interventions for reducing road traffic injuries and deaths in both rural and urban settings. Considering continuing increases in traffic volume worldwide, automated enforcement with speed cameras to curb aberrant speeding behaviour, is a rational intervention to augment or supersede conventional enforcement. Speed cameras used for road section control, which measure average speed over distance, together with related emerging technologies arguably have the potential to favourably influence speeding behaviour and thus enhance road safety.
Implications for research
The results of this systematic review are consistent across studies, showing that speed cameras do reduce road traffic crashes, as well as those resulting in road injuries and deaths. However, in this study, an overall magnitude or significance of this effect could not be deduced because of heterogeneity in background information and road and traffic related factors. An extensive literature exists on issues pertaining to speed cameras. Nonetheless, when searching for studies we found numerous uncontrolled before after studies, many studies without any 'before' data and no randomised controlled trials. For the future, interventions using speed cameras and related automatic speed enforcement devices need to be scientifically evaluated using well designed trials, conducted over sufficient time, with several data collection points and controls where possible. These studies also need to clearly show how potential study bias and confounding is controlled, and use standardised study analyses and outcome methodology, so that their true effectiveness can be more accurately assessed. Ideally, this can be more readily achieved if road safety authorities and academic research entities collaborate in the conduct of automated speed enforcement studies through all phases, from program planning to program completion.Get full text at The Cochrane Library
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