Investigating Time Halo Effects of Mobile Photo Enforcement on Urban Roads

This paper investigates the time halo effects of mobile photo enforcement (MPE) on urban arterial and collector roads. Speed data were continuously recorded at nine locations for five consecutive weeks during the summer months of 2015 in Edmonton, Alberta, Canada. Each location was enforced according to a predefined deployment plan related to the regular working hours of MPE personnel. A time series intervention analysis that used percentages of speed limit violations was conducted to determine and to understand the time halo effects of MPE. The results of the analysis indicate that time halo effects existed at all study locations and that significant reductions in speed limit violations occurred because of MPE. The authors concluded that, on average, if an MPE unit was deployed eight times during a week for 22 h (approximately 2.7 h per visit) at an urban location, it would produce a time halo effect that would extend for approximately 5 days and reduce speed limit violation rates by almost 19%. In addition, the number of enforcement visits per week, the number of enforcement hours per week, and the average hours per visit were found to be strongly correlated to the longevity of the time halo effects and the reduction in speed limit violations. The findings of this study can be used to significantly increase the coverage of MPE programs and the safety benefits associated with MPE operations.