As a vehicle approaches the radar unit, it enters its operating zone or "zone of influence." The length and width of the zone depends on such factors as the strength of the signal and the transmittor height above the ground. The unit will record the speed of only one vehicle at a time, determined by the vehicle presenting the best target by reason of reflecting surface, position, or speed. Based on this, many courts have pointed out possible defenses to proof of speed by radar. One court has stated in its opinion there are many more defenses that can be interposed to radar speed interception than to motorcycle apprehension.
William K. McCarter, Legal Aspects of Police Radar, 16 Clev.-Marshall L. Rev. 455 (1967)