The study arose from concern about degraded system performance as a consequence of electromagnetic interference and from interest in recent years about the possible effect on the human body of the various electromagnetic fields generated by electronic transmitting equipment. Field strengths were measured with a calibrated probe at 10 locations in the test vehicle, with and without the driver's door open and with and without occupation of the front seat. The frequencies tested represented the bands of 25 to 50, 150 to 174, 400 to 512, and 806 to 866 megahertz. Levels of output power are given for the data presented. Field-strength levels are also given for when a metallic prisoner shield or a personal transceiver is used in a vehicle together with a mobile transceiver, in some cases. Photographs, diagrams, a list of six references, and an appendix discussing field strength measurements of radar devices used to measure speed are included. (Author abstract modified)