Traffic Enforcement Camera EffectivenessUK-Based Studies
In the UK, the effectiveness issue has become particularly contentious since the introduction of Safety Camera Partnerships. Studies in the UK have provided analysis of the effects of speed cameras deployed by Safety Camera Partnerships. An initial three-year study commissioned by the Department for Transport (DfT) [17] showed that vehicle speeds dropped by seven percent at sites where cameras were installed and claimed that "at camera sites, there was also a reduction of over 100 fatalities per annum (40% fewer). There were 870 fewer people killed or seriously injured and 4,030 fewer personal injury collisions per annum. There was a clear correlation between reductions in speed and reductions in PICs" (personal injury collisions). The three year DfT report was criticised in some quarters for giving only a small amount of attention to the phenomenon of regression to the mean (RTM). Since the cameras were placed at sites where a high number of accidents had been observed, a lower number of accidents might be expected in subsequent years simply by random chance. Professor Mervyn Stone of the The Department of Statistical Science at University College London was commissioned by the BBC Radio Four Today Programme to write a report[11] about UK speed cameras and also Traffic Calming. His report criticises some of the methodologies used in some speed camera studies (including the DfT three year report) and in particular he mentions the RTM effect. A follow-up four-year independent study commissioned by the DfT [18] concluded "after allowing for the long-term trend, but without allowing for selection effects (such as regression-to-mean) there was a 22% reduction in personal injury collisions (PICs) at sites after cameras were introduced. Overall 42% fewer people were killed or seriously injured. At camera sites, there was also a reduction of over 100 fatalities per annum (32% fewer). There were 1,745 fewer people killed or seriously injured and 4,230 fewer personal injury collisions per annum in 2004." In addition, the four year report includes statistical modeling of the RTM effect based on a reduced set of camera sites for which suitable data was available (see [19] appendix H --- tables H3 and H7). Rural roads were excluded from the RTM modeling, because of difficulties establishing representative models for such roads, although the report does state it is likely that RTM effects will be larger for rural roads because expected collision frequencies tend to be lower than on urban roads. The report urges caution in drawing too strong conclusions from a small data set. Based on the RTM modeling undertaken the report suggests that for personal injury collisions (non-serious collisions resulting in injuries) a 16.2% reduction in injuries was due to the cameras, a 6.7% reduction was due to regression to the mean and a 7.9% reduction was due to the general downward trend in accidents over the period. For fatal and serious collisions, the modeling estimated a 10.4% reduction in such collisions due to the cameras, a 34.8% reduction due to regression to the mean and a 9.3% reduction due to general downward trends in accident rates. A 2006 DfT report "Contributory factors to road accidents"[12] uses STATS19 data to analyse accidents have speed as a contributory factor. The factors "exceeding the speed limit" or "going too fast for conditions" were judged by officers at the scene of road accidents. It was suggested that "exceeding the speed limit" would be marked as a cause if the officer had reason to believe from external evidence (for example "skid marks on the road") that the driver was doing so. Exceeding the speed limit was said to be a factor in 12% of fatal road accidents and 5% of all road accidents. An independent UK-based controlled study[13] uses STATS19 data to show that speed cameras are effective at reducing accidents and injuries but added that wider deployment would improve their effectiveness. Two 2006 UK studies have questioned the accuracy of STATS19 data when used to look at serious injury rates since there is ambiguity in whether an injury is judged serious or minor and the UK police records do not match hospital admission records. The first study "Changes in safety on England’s roads: analysis of hospital statistics", published by the British Medical Journal[14] concludes that "the overall fall seen in police statistics for non-fatal road traffic injuries probably represents a fall in completeness of reporting of these injuries". The second study "Under-reporting of Road Casualties – Phase 1", published by the DfT,[15] recommends that reports should not rely solely on STATS19 injury data (none of the reports mentioned do). In addition, some UK police officers have confirmed that speed cameras do not reduce casualties, they are just for revenue generation[16]. US-Based Studies
In the United States, questions of effectiveness have centered on the more common red light cameras. A number of government-sponsored studies have addressed the question of whether, on balance, the devices produce a safety benefit. A U.S. Safety Evaluation of Red-Light Cameras, for example, found that red light cameras led to a decrease in right-angle crashes and a smaller increase in the number of rear-end collisions. The study applied estimates from a 1997 study of the cost of accidents based on severity to conclude the cameras yielded a positive overall cost benefit from a reduction in more expensive right-angle injury collisions. A 2005 Virginia Department of Transportation study of the long-term effect of camera enforcement in the state found a decrease in the number of right-angle crashes, but an increase in rear-end crashes and an overall increase in the number of accidents causing injuries. The report recommended further study of the issue to determine whether the severity of the eliminated red light running crashes was greater than that of the induced rear-end crashes. The department released a more extensive evaluation of the data in 2007 which showed that the overall number of accidents at intersections with red light cameras increased in four of the five cities using the technology. Fairfax City reported a 7% drop in the overall number of accidents and a 5% drop in injury accidents while overall the state's cameras were correlated with a 29% increase in overall accidents and an 18% increase in injury accidents. (Study text in PDF). This study also notably found that red-light violations decreased by 94% at one Fairfax County intersection, after the advent of a 1.5 second longer yellow-light cycle.[17] A 2004 Texas Transportation Institute study found, "crashes decrease with an increase in yellow interval duration and a reduction in speed limit." After 1.0 second was added to the yellow signal timing at test intersections, accidents dropped by 35 to 40%. This compares with a 6.4% reduction for "area-wide officer enforcement of intersection traffic control devices... during the time of the enforcement activity" (Study text in PDF). A 2005 study of the Raleigh, North Carolina red light camera program conducted by the Institute for Transportation Research and Education at North Carolina State University compared “before” and “after” red-light camera intersection data and found right-angle crashes dropped by 42 percent, rear-end crashes dropped by 25 percent and total accidents dropped by 22 percent. ([20]) In the state of Victoria, Australia, widespread and increased use of speed cameras has given rise to public criticism over whether the collection of over $400 million in speed camera revenue during the 2003-04 financial year raises questions of fairness and equity. With drivers being fined for speeding at only a few km/h above the speed limit and receiving the infringement notice up to months later, many have questioned whether there may be education and enforcement measures available that place less of an imposition on motorists. References
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