The use of alcohol safety interlocks on the vehicles of impaired driving offenders has been growing over the last decade in the United States and Canada. Current versions of this device, which requires the operator to provide a breath sample for analysis before being able to start the vehicle, have proven to be highly resistant to circumvention. However, safeguards in the inter- lock unit itself do not prevent circumvention with a noninterlock vehicle. This paper reports on a study of the effect on interlock vehicle use and the availability of noninterlock vehicles among 2260 interlock users in Alberta, Canada. More than half of the interlock program participants had access to a noninterlock vehicle in the family. Those offenders made fewer trips in the interlock vehicle; however, there was little evidence about whether they were driving the noninterlock vehicles when drinking.