The so-called interlock effectiveness studies, which stretch back over the last 20 years, typically involve comparing matched groups of offenders. One group has alcohol interlock devices installed in their vehicles and the other group is simply under suspension or revocation. The studies assess the differences in terms of recidivism rates, or the extent to which the people in each of those groups are caught for subsequent drinking and driving offences.
In those studies, the interlock group invariably does better--not just a little bit better, but much better. Why? It's because interlocks are effective in making responsible decisions about driving after drinking for people who can't make them on their own.
We actually did an assessment ourselves of the number of times alcohol interlocks installed in the vehicles of offenders in Canada have prevented driving after drinking. In 2008 alone it was more than 193,000 times.