Some researchers have argued that penalties are not effective deterrents if the probability of apprehension for an arrest is extremely low. The Canadian Parliament's passage of a law permitting police to demand a breath sample and administer a roadside breath test to a driver suspected of drinking provided an opportunity for increasing public awareness of the new law and for increasing their subjective arrest probabilities. An information campaign was developed to inform the Canadian public of the change in the law. A continuous logarithmic scale of probabilities was developed and tested; results showed that persons could make estimates of their chances of being arrested. Subjects estimated that the average driver's chances of being arrested were 1 in 427, and that their own chances of arrest were 1 in 12,882. Subjects also reported that they would stop driving after drinking if the chance of arrest was 1 in 525. Thus, people needed to be convinced to view themselves as they viewed the average driver if they were to change their driving behavior. The four scales used in this phase of the research were also used to assess the effectiveness of the information components produced by an advertising agency. A total of 450 persons viewed or read television commercials, newspaper advertisements, or a press release in the advertising agency's test center. Results indicated that the information produced a change in the subjective probability of arrest when it was presented to this captive audience. The results of the evaluation of the field information campaign are incomplete and will prove whether or not the campaign has been effective. Charts, footnotes, and eight references are provided.