An additional benefit of the greater use of semimarked cars would be better performance with respect to speed and acceleration. In 1982 the Illinois Department of Law Enforcement compared 60 semimarked vehicles with 60 units marked with visabars. The units worked on similar patrols and had similar workloads. The officers in the semimarked cars achieved better fuel mileage and had fewer and less severe accidents than those in marked units. They also achieved higher productivity in the issuance of citations for speeding. Officers perceived that the semimarked cars had a higher degree of public approval, greater productivity, better performance, and little impact on voluntary compliance with laws. They also noted greater difficulty in vehicle recognition by the public and some reduction in safety to the driver and the motoring public. However, at least half of the officers perceived no difference in safety between the two types of vehicles. In addition, 90 percent of the responding officers did not want visabars put on their semimarked units, 4 percent were undecided, and 6 percent would prefer a visabar. Data tables, four footnotes which contain references, and appendixes presenting the study instrument and comments from the 50 officers surveyed are provided.