Several unmanned radar devices were installed on I75 in northern Kentucky in an attempt to reduce speeds. It was assumed that drivers use radar detectors to exceed the speed limit with a resulting variance between their speeds and others in the traffic stream. Therefore, a reduction in overall speeds and variance was expected to reduce the probability of accidents. Historical data indicated an unusually high accident rate for the study area.

Emphasis was placed on collection and analysis of speed-related data. In addition, a survey of radar detector usage was made and accident patterns were documented.

Speed measures analyzed 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 traveling 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 while the speeds of vehicles without detectors were not affected. Radar detector usage was found to be 42 percent in trucks and 11 percent in cars. When comparing accident data three years before and one year after truck diversion and unmanned radar installations, there was a reduction in truck-related and speed-related accidents.

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The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, of the Kentucky Transportation Cabinet, nor of the Federal Highway Administration. The report does not constitute a standard, specification, or regulation.