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Maryland Ignition Interlock License Restriction

Maryland Ignition Interlock License Restriction is a statewide license restriction program for drivers with multiple alcohol-related traffic offenses that is designed to reduce alcohol-impaired driving recidivism. 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.

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.

The qualifying studies for Blueprints were Beck et al. (1999) and Rauch et al. (2011), which conducted evaluations of the program in the state of Maryland by randomly assigning 1, 387 and 1,927 drivers to treatment or control groups, respectively. 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, and this benefit was maintained in the following year after system removal. Results for Rauch et al. (2011) showed that drivers with two years of interlock installation, relative to controls, had a lower hazard of committing an alcohol-related offense with sustained effects two years following the intervention period.

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.

Read the Program Fact Sheet

Return to Blueprints Bulletin Issue 8. December 2018.


Blueprints for Healthy Youth Development
University of Colorado Boulder
Institute of Behavioral Science
UCB 483, Boulder, CO 80309


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Blueprints for Healthy Youth Development is
currently funded by Arnold Ventures (formerly the Laura and John Arnold Foundation) and historically has received funding from the Annie E. Casey Foundation and the Office of Juvenile Justice and Delinquency Prevention.