• October 5th, 2014

A study is described that was undertaken to examine the effects of patrol tactics on vehicle speeds, to identify the best patrol tactics of those studied, to identify general speed trends over time, and to examine the effects of an areawide selective enforcement program implemented by the Alabama State Highway Patrol. Both two- and four-lane roads were examined. Six patrol tactics were investigated–four single-vehicle tactics and two dual-vehicle tactics. All data were gathered from a radar-equipped van operated in a moving mode. Vehicle speed characteristics examined included mean speed, 85th percentile speed, and speed variance. Mean speeds were more affected by patrol tactics than were 0.85 percentiles or variances. Statistically significant reductions in average speeds were obtained with all tactics that used marked patrol vehicles. The largest reductions in average speed occurred with the stationary tactic. Significant reductions in 0.85 percentile speeds were obtained for all tactics on the four-lane road but for none of the tactics on the two-lane road. Variances were generally not affected on the four-lane road, whereas on the two-lane road they increased for five of the six tactics studied. Overall, the most effective tactic was the marked stationary vehicle. The unmarked patrol vehicle, even when issuing citations, had little, if any, effect on the speed parameters. A greater halo effect on speeds occurred on the two-lane than on the four-lane road. The general areawide selective enforcement program may have reduced mean speeds on the four-lane road but did not affect speeds on the two-lane road. No trends or cumulative effects on speeds were found during the three-month selective enforcement period. (Author)