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Maryland Ignition Interlock License Restriction (Policy)

Blueprints Program Rating: Model

A statewide license restriction program for drivers with multiple alcohol-related traffic offenses to reduce alcohol-impaired driving recidivism.

  • Department of Transportation National Highway Traffic Safety Administration
  • 1200 New Jersey Avenue SE
  • Washington, DC 20590
  • www.nhtsa.gov/
  • Adult Crime

    Program Type

    • Adult Crime Prevention
    • Police Crime Prevention

    Program Setting

    • Community (e.g., religious, recreation)

    Continuum of Intervention

    • Indicated Prevention (Early Symptoms of Problem)

    A statewide license restriction program for drivers with multiple alcohol-related traffic offenses to reduce alcohol-impaired driving recidivism.

      Population Demographics

      Adult drivers with multiple alcohol-related driving offenses whose licenses have been revoked or suspended and who were later approved for a restricted license to drive an interlock-equipped vehicle.

      Age

      • Adult

      Gender

      • Male and Female

      Race/Ethnicity

      • All Race/Ethnicity

      Opportunity to drive or start a vehicle while alcohol impaired

      • Individual

      The use of ignition interlock license restrictions requires those with previous alcohol-related driving offenses to pass a breath analyzer test of blood alcohol levels before starting a vehicle. The program further requires that drivers who are applying for reinstatement of their driving licenses install the ignition interlock system in their vehicle and continue to use it for two years before they are eligible for reinstatement.

      Note: The State of Maryland evaluated the effects of interlock installation in two studies. Both were RCTs and carefully conducted. One involved one year of installation and one study two years. Both found large reductions during installation. The one-year study did not show sustained effects, while the two year study did. Thus, Blueprints is certifying only the two-year study.

      The use of ignition interlock license restrictions requires those with previous alcohol-related driving offenses to pass a breath analyzer test of blood alcohol levels before starting a vehicle. By using this automated system, intersecting risk behaviors (drinking and driving) are controlled, rather than either behavior separately. The program further mandates that drivers who are applying for reinstatement of their driving licenses install the ignition interlock system in their vehicle and continue to use it for two years before they are eligible for reinstatement.

      The ignition interlock device requires a potential driver to blow into a breath alcohol sensor connected to the vehicle's ignition system before the vehicle's engine will start. An on-board computer analyzes the alcohol concentration of the driver's breath and compares it to a set point, usually .02 grams per deciliter. If the alcohol concentration is above the set point or the driver does not provide a breath sample, the interlock prevents the vehicle engine from starting.

      Ignition interlocks are comprised of four basic elements:

      1. A breath alcohol sensor installed in the passenger compartment of a vehicle and connected to a control unit in the engine compartment that allows the engine to start only upon an acceptable breath test;
      2. A tamper-proof system for mounting the control unit in the engine compartment;
      3. A data-recording system that logs breath test results, tests compliance, and collects other state-mandated data; and
      4. A retest system which, after the engine has started, requires the driver to provide additional breath samples (generally every 10 to 15 minutes) to ensure that the driver remains alcohol-free. Several minutes are provided for the driver to exit traffic and move to a safe location for retesting.

      By addressing the combined behaviors of driving and drinking, the ignition interlock system bypasses disincentives that are presumed to motivate the alcohol-intoxicated driver and reduce unsafe driving.

      • Behavioral

      The two qualifying studies for Blueprints were Beck et al. (1999) and Rauch et al. (2011). Beck et al. (1999) randomly assigned 1,387 individuals who had previously lost their driving licenses due to alcohol-related offenses and were applying to have their licenses reinstated to either a control group (n = 689) or the treatment group (n = 698). Those in the treatment group were required to have the ignition interlock system installed in their vehicles and to maintain the system for one year. The study then followed the participants for two years to measure alcohol-related traffic violations.

      Rauch et al. (2011) followed a similar study design, randomly assigning 1,927 drivers to the treatment (n = 944) or control (n = 983) group. However, Rauch et al. (2011) required drivers to use the ignition interlock system for two years (as opposed to one in Beck et al., 1999) and monitored the outcomes for an additional two years after completion of the intervention.

      Beck et al. (1999) reported that drivers with the ignition interlock system were significantly less likely to recidivate in the year in which they had the system installed as compared to the control group. In the next year, the treatment and control groups did not differ significantly on alcohol-related traffic violations, but first-year benefits were maintained. Rauch et al. (2011) found a similar positive program effect on drivers during the two years of the intervention period and a smaller, but still significant, effect in the two years after the intervention.

      Drivers with one year of interlock installation, relative to controls, had (Beck et al., 1999):

      • lower risk of receiving an alcohol-related traffic violation (2.4% versus 6.7%)
      • no sustained effect in the year after the ignition interlock system was removed

      Drivers with two years of interlock installation, relative to controls, had (Rauch et al., 2011):

      • 36% lower hazard of committing an alcohol-related offense
      • sustained effects two years following the intervention period, with a 32% lower hazard rate

      The studies did not report formal mediator analysis.

      Beck et al. (1999) reported a small effect size in favor of treatment. That is, in the year the treatment group had the ignition interlock system in place, treatment group participants had .36 lower relative risk of an alcohol-related traffic violation than the control group. Rauch et al. (2011) also reported a small effect size favoring the treatment group. Results showed a 1.57 higher hazard of an alcohol-related offense among the control group (compared to the treatment group) in the two years of the intervention period.

      The samples used in Beck et al. (1999) and Rauch et al. (2011) were medium-large and from Maryland.

      Beck et al. (1999)

      • The study used police records, which capture only a small portion of intoxicated driving
      • Significance tests for baseline equivalence did not include measures of past alcohol abuse and driving records
      • Outcome equals zero at baseline in survival models but no controls for past alcohol use or driving offenses

      Rauch et al. (2011)

      • The study used police records, which capture only a small portion of intoxicated driving

      See Ignition Interlock in database for generic version of the program.

      • Blueprints: Model

      Beck, K. H., Rauch, W. J., Baker, E. A., & Williams, A. F. (1999). Effects of ignition interlock license restrictions on drivers with multiple alcohol offenses: A randomized trial in Maryland. American Journal of Public Health, 89, 1696-1700.

      Rauch, W. J., Ahlin, E. M., Zador, P. L., Howard, J. M., & Duncan, G. D. (2011). Effects of administrative ignition interlock license restrictions on drivers with multiple alcohol offenses. Journal of Experimental Criminology, 7, 127-148.

      Eileen Michelle Ahlin, Ph.D., Evaluator
      Criminal Justice School of Public Affairs
      Penn State Harrisburg
      (717) 948-4341
      ema105@psu.edu

      Kenneth H. Beck, Ph.D., FAAHB, Evaluator
      School of Public Health
      University of Maryland
      kbeck1@umd.edu

      Study 1

      Beck, K. H., Rauch, W. J., Baker, E. A., & Williams, A. F. (1999). Effects of ignition interlock license restrictions on drivers with multiple alcohol offenses: A randomized trial in Maryland. American Journal of Public Health, 89, 1696-1700.

      Study 2

      Rauch, W. J., Ahlin, E. M., Zador, P. L., Howard, J. M., & Duncan, G. D. (2011). Effects of administrative ignition interlock license restrictions on drivers with multiple alcohol offenses. Journal of Experimental Criminology, 7, 127-148.

      Beck, K. H., Rauch, W. J., Baker, E. A., & Williams, A. F. (1999). Effects of ignition interlock license restrictions on drivers with multiple alcohol offenses: A randomized trial in Maryland. American Journal of Public Health, 89, 1696-1700.

      Evaluation Methodology

      Design:

      Recruitment: The study recruited Maryland drivers with multiple alcohol traffic offenses whose licenses had been revoked or suspended and who were later approved for relicensing by the state Medical Advisory Board.

      Assignment: Participants were randomly assigned to either the business-as-usual control group (n=689) or the ignition interlock system treatment group (n=698). The control group received a probationary license agreeing not to drive after consuming any alcohol and participating in Maryland’s Drinking Driving Monitoring Program, which involves reporting to a probation monitor. The treatment group was required to install the ignition interlock device and was also informed about treatment and support programs, in which they were required to participate.

      Attrition: The subjects were followed for 1 year after the program start, until the end of the required period of use of the interlock device, and then for 1 more additional year. Of the 1,387 participants, 23 moved out of state during the study, but all were followed for the purposes of analysis.

      Sample: The sample was predominately male (88-91%) and white (82-86%). The median age was 33; participants ranged from ages 19-75.

      Measures: The study used police records on whether participants received subsequent alcohol-related traffic violations.

      Analysis: The study used relative risk analysis and proportional hazard survival models to compare the rate of recidivism in the treatment and control groups. The multivariate survival models controlled for demographic covariates but not for baseline measures of past alcohol use and driving offenses.

      Intent-to-Treat: All randomized participants were included in the analysis.

      Outcomes

      Implementation Fidelity: Of the total sample, 14% (n=98) failed to comply with the treatment requirements and remained suspended. About 57% installed the device, and an additional 23% signed a waiver stating that they did not own a vehicle and would not drive other vehicles without the ignition interlock system, and 7% signed a waiver for the restriction period, but had an interlock system installed later.

      Baseline Equivalence: All participants had multiple previous alcohol-related driving offenses. The number of previous alcohol traffic violations did not differ between the interlock group (mean = 3.57, SD = 1.43) and the control group (mean= 3.61, SD = 1.33). Table 1 shows no significant differences on the demographic measures.

      Differential Attrition: With all subjects followed, there was no attrition.

      Posttest: Within the year after assignment, those in the control group had a significantly higher risk of receiving an alcohol-related traffic violation than those in the treatment group (6.7% versus 2.4%, .36 relative risk for the treatment group).

      Long-Term: In the year after the ignition interlock systems were no longer required, there were no significant differences in the outcome measure between the treatment and control groups. Over the full 2-year period, however, the program benefits for alcohol-related traffic violations remained significant (9.1% in the control group versus 5.9% in the intervention group, and .64 relative risk for the treatment group).

      Rauch, W. J., Ahlin, E. M., Zador, P. L., Howard, J. M., & Duncan, G. D. (2011). Effects of administrative ignition interlock license restrictions on drivers with multiple alcohol offenses. Journal of Experimental Criminology, 7, 127-148.

      Evaluation Methodology

      Design:

      Recruitment: The study followed the protocol established in Study 1 by recruiting Maryland drivers who had two or more alcohol traffic offenses and who had been approved for reinstatement of their driver's license by the state’s Medical Advisory Board.

      Assignment: Participants were randomly assigned to either the control group (n=983) or the ignition interlock system treatment group (n=944). Drivers assigned to the control group reported to a probation monitor and enrolled in Maryland’s Drinking Driver Monitor Program. The treatment group was enrolled in the interlock license restriction program and had 30 days to have the interlock installed.

      Attrition: The study waited until 6 years after the start to assess subjects during the 2 years of the program and during the 2 years following the program end. Of the 1,927 participants, a total of 58 drivers died (3.0%) and 68 moved out of state during the study (3.5%).

      Sample: The mean age of the sample was 40 years at the start of the program and the sample was predominately male (88%). The sample was comprised of 80% white, 15% black, 1% Asian, and 4% other/unknown participants.

      Measures: The study used all alcohol-related violations, including any arrest for DUI or DWI that resulted in a preconviction administrative sanction, a conviction, probation before judgment, or their combination as reported by state legal records.

      Analysis: The study conducted Kaplan-Meier survival analysis to compare the proportion of the samples that did not receive alcohol-related traffic violations. The authors also used proportional hazard models to estimate the effects of potential risk factors on the probability of alcohol-related violation-free survival during the study period, including age, sex, race, prior alcohol-related violations at program enrollment, and the violation disposition category. Finally, the study estimated a hazard ratio for the outcome measure.

      Intent-to-Treat: All participants assigned to the treatment were included in the analysis. The models treated subjects who died or moved out of state as censored.

      Outcomes

      Implementation Fidelity: The treatment participants stayed in the program an average of 23 months, while the control group remained an average of 21 months. For the treatment group, 22% of the subjects failed to comply by installing the interlock ignition system or obtaining a waiver.

      Baseline Equivalence: The study reported no significant differences between treatment groups for demographic measures, the number of previous alcohol-related offenses, or the prior violation disposition category.

      Differential Attrition: There was no significant difference across conditions in the likelihood of dying or moving from the state. The study did not provide further analysis, but the attrition rate was low.

      Posttest: After controlling for age, gender, race/ethnicity, and prior offenses, the study found that in the 2-year intervention period, the treatment group had a 36% lower hazard of committing an alcohol-related offense.

      Long-Term: In the two years following the intervention period, the treatment group had 26% lower hazard of committing an alcohol-related offense and a 32% lower hazard over the entire 4-year period.