Since April 1978, the Illinois State Police has been patrolling rural portions of interstate highways by using fixed-wing aircraft. When used for patrol, the aircraft quickly cover long sections of highway, searching out accidents, stranded motorists, traffic bottlenecks, and traffic law violators. As indicated by the analyses of the first year of operations, aerial patrol successfully reduces accidents in a cost-beneficial manner. There were 18 percent fewer accidents in the areas patrolled by the aircraft than expected from traffic trends. Serious accidents (fatal and personal injury) were 24 percent fewer than expected. Both decreases are statistically significant at the 99 percent level of confidence. Further, a benefit-cost ratio of 9.1 to 1 was calculated by using the National Safety Council's cost estimates for traffic accidents. The success of this operation is attributed to the fact that 3,243 citations were issued to drivers speeding over 70-mph, who were ticketed because of the aerial patrol. These flagrant violators, and particularly other motorists who observed the ticketing, subsequently probably drove more cautiously and avoided situations that might have resulted in accidents. The results also indicate that for the aerial patrol to realize its full potential of reducing accidents and lowering vehicle speeds, more ground units are needed on these highways than originally anticipated. Statistical charts and graphs and data from the cost-benefit analysis are appended. (Author abstract modified)