Drinking and Driving

The deterrence of drinking and driving depends primarily on increasing the perceived probability of apprehension in the target population. One way of accomplishing this is to introduce laws that replace the vague offense of "driving under the influence" with the offence of driving with a BAC above a prescribed level (usually .08 or .05). Another way is to initiate a police crackdown on drinking and driving for a period of time. The experience of the United Kingdom in 1967, when it introduced for the first time a .08 BAC limit, illustrates well the usual impact of such interventions. The law was extremely controversial at the time, with the result that most drivers were aware of it and believed they would be caught if they drove after drinking. There was a marked decline in serious accidents at nights and weekends, but not at times when drinking and driving would not be expected. However, the deterrent impact wore off within a few years as drivers gradually became used to the new law, and realized that their chances of detection were in fact not very high.

This pattern of a sharp decline in drinking and driving coincident with a new law or with intensified police enforcement, followed by a gradual decline to pre-intervention levels, is commonly found. Deterrence is an unstable psychological process dependent on continuous publicity and on the perception of a credible police threat. However, random breath testing (RBT) is a major exception to the rule that enforcement effects are invariably temporary.

Under RBT as it is practiced in Australia and some Scandinavian countries, large numbers of motorists are pulled over at random by police and required to take a preliminary breath test, even if they are in no way suspected of having committed an offense or been involved in an accident. Thus RBT should be sharply distinguished from the U.S. practice of sobriety checkpoints, in which police must have reasonable suspicion of alcohol consumption before they can require a test. The RBT law has been very extensively advertised and vigorously enforced in Australia, with the result that 82 percent of motorists reported in 1999 having been stopped at some time (compared with 16 percent in the United Kingdom and 29 percent in the United States).

Time series analyses of accidents show that in Australia RBT had an immediate, substantial, and permanent impact, with every extra one thousand tests conducted each day by police resulting in a 6 percent decline in daily serious accidents (Henstridge et al.). The direct deterrent impact was enhanced by the fact that RBT gave heavy drinkers a legitimate excuse to drink less when drinking with friends. This is a good example of how formal sanctions can reinforce informal sanctions.

The same time series analyses show that a reduction in the legal BAC in some states from .08 to .05 resulted in an average 10 percent decline in serious accidents. This is consistent with experience in other countries where the BAC level has been reduced.

RBT and lower BAC levels concern certainty of detection. Administrative license revocation, the practice in some U.S. states where drivers who drink have their licenses revoked almost as soon as they fail a breath test, concerns swiftness of punishment. Research supports the potential of this procedure to reduce the recidivism of sanctioned drivers and to deter others. As a general rule, the only sanction applied to drivers who drink that reduces recidivism is loss of license. Although many drivers continue to drive while unlicensed, they tend to be more cautious and hence safer. Thus it seems that license loss has (to some extent) a physically incapacitating effect.