Behavioral measures of drinking: patterns from the Alcohol Interlock Record

This report reviews breath test data captured by the alcohol ignition interlock, a device that prevents a car from starting when BAC (breath alcohol concentration) is elevated.

The predictors were elevated BAC test rates from ignition interlock equipped cars of traffic offenders convicted of DUI (driving under the influence of alcohol) and who used interlocks for 6-18 months. Outcome data were future DUI convictions.

Québec and Alberta, Canada.

Approximately 10000 interlock users from these two culturally distinctive English- and French-speaking Provinces.

Predictor patterns were analyzed from among 23 million breath tests. Repeat DUI convictions accumulated up to several years after interlock removal were studied as an outcome to be predicted by the rate of BAC tests > or = 20 mg/dl (0.02%) while the interlock was installed. Data were analyzed with sensitivity and survival methods.

A median of eight interlock breath tests per day per driver were logged (a rate of 3000 tests/year). Less than 1% of all tests were over 0.02%, but the rate of elevated BAC tests, particularly those taken at 7-9 a.m., strongly predicts repeat DUI offenses 2 years hence. The interlock record is an unobtrusive measure of drinking behavior and can be used to profile driver risk.

With new legal mandates, North American use of these DUI control devices is increasing rapidly from the current 5% penetration rate. Interlock data may eventually come to serve as a useful adjunct for patient monitoring by alcohol counselors as well as by courts and motor vehicle authorities.