Study
Beck and colleagues (1999) used a randomized controlled trial to examine the effects of ignition interlock license restrictions in preventing recidivism in a group of Maryland drivers who had multiple alcohol-related driving offenses. Study participants were limited to those convicted of multiple alcohol-related offenses and defined as drivers who had committed two or more alcohol traffic violations in the previous 5 years or three or more such violations in the previous 10 years. Participants had their licenses revoked or suspended but had been approved for relicensing by Maryland’s Medical Advisory Board. Participants who were recommended for relicensing were randomly assigned to the interlock program (
n
= 698) or to the control program (
n
= 689).
The study sample was predominately male (90 percent) and white (84 percent), with an average age of 33. There were no significant differences between the groups on basic demographic characteristics. There were also no significant differences in the average number of previous alcohol violations (3.57 for the interlock program group and 3.61 for the control group).
Study participants assigned to the interlock program were notified by letter that they were approved for license reinstatement only if they agreed to a restriction prohibiting them from operating a vehicle without an interlock device for 12 months. This restriction was noted on their licenses. Interlock program participants had 45 days to get the device installed. They were also informed about treatment or support programs (e.g., Alcoholics Anonymous) that they were required to participate in. Failure to comply with any of these conditions of the program resulted in a suspension of driving privileges. Study participants assigned to the control program were notified by letter that they must comply with the restriction ordinarily placed on persons convicted of multiple alcohol offenses, including a driver’s license restriction stating that they may not drive after drinking any amount of alcohol. Most often, these restrictions included mandatory participation in Maryland’s Drinking Driving Monitoring Program, which required drivers to report regularly to a court-approved probation monitor who determined if the person was complying with the required treatment programs and whether the person was drinking or taking drugs. Failure to comply with the conditions resulted in suspension of driving privileges.
Each case was tracked by the Maryland Motor Vehicle Administration, which closely monitored compliance. The primary outcome measure of interest was whether the permitted committed an alcohol traffic violation during the first year after entering the study (defined as 365 days after notification), the period during which the interlock license restriction was in effect and the device was required to be in the vehicle. Alcohol traffic violations were also examined during the second year (defined as beginning 366 days after notification and ending 365 days later), the period during which the license restriction had been lifted and the device would be removed. The data was analyzed from a relative risk perspective.
Study
Rauch and colleagues (2011) conducted a randomized controlled trial to test the effectiveness of Maryland’s use of ignition interlock to reduce alcohol-related violations. Drivers included in the study had two or more alcohol-related traffic violations in their lifetime. A total of 1,927 persons applied for reinstatement of a Maryland driver’s license during 2000 and 2001. The Medical Advisory Board in Maryland randomly assigned 944 of them to the ignition interlock group and 983 to the control group.
The two groups did not differ on any of the demographic or offense dimensions. The study sample was predominately male (88 percent) and white (80 percent), with an average age of 40. Participants in both groups had an average of 3.3 alcohol-related priors.
Members of the control group were required to participate in the Drinking Driver Monitor Program. As part of this program, individuals routinely reported to a probation monitor who supervised participant compliance with the program and overall sobriety, administered breathalyzer tests, and ensured participant attendance at self-help or treatment meetings. All participants, no matter their assignment, were prohibited from operating a motor vehicle with any alcohol in their system. The program lasted 2 years, and the researchers followed participants for an additional 2 years after drivers left the program.
The outcome of interest was alcohol-related violations, which included a preconviction administrative sanction, a conviction, probation before judgment, or a combination thereof. Data was provided by the Motor Vehicle Administration.
To accommodate the time lag between a violation and its final disposition and appearance on a record, researchers began data analysis 6 years after the last driver was enrolled in his or her respective program. Researchers used an intent-to-treat approach for analysis. Cox’s proportional hazard models were used to control for independent variables (driver age, sex, race, prior alcohol-related violations, and violation disposition category) that might influence the probability of reoffending. Additionally, statistical adjustments were made to take into account differences in program duration between the control group (21 months) and the experimental group (23 months). Subgroup analyses were conducted on age, race, and prior alcohol-related offenses.
