Several unmanned radar devices were installed on interstate 75 in northern Kentucky in an attempt to reduce speeds. It was assumed that drivers use radar detectors to exceed the speed limit thus causing a variance between their speeds and those of others in the traffic stream. Since historical data indicated an unusually high accident rate for the study area, a reduction in overall speeds and variance was expected to reduce the probability of accidents. The high accident rate also resulted in a plan to reduce trucks on I-75 in the study area by diverting them onto a bypass route (I-275). Emphasis was placed on collection and analysis of speed-related data. In addition, a survey of radar detector use was made and accident patterns were documented. Speed measures analysed included mean speed, standard deviation in speed, numbers of vehicles exceeding specified speed levels, and 85th percentile speed. Results indicate that unmanned radar was an effective means of reducing the number of vehicles travelling at excessive speeds. The differences in mean speeds were small and the impact of unmanned radar was less obvious than it was for the percentage of vehicles exceeding speed levels of 65, 70, 75, and 80 mph. The speeds of vehicles with radar detectors decreased significantly as a result of unmanned radar, whereas the speeds of vehicles without detectors were not affected. Radar detector use was found to be 42% in trucks and 11% in cars. When comparing accident data 3 years before and 1 year after truck diversion and unmanned radar installations, there was a reduction in truck-related and speed-related accidents.
Abstract