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Effects of Ignition Interlock License Restrictions on Drivers with Multiple Alcohol Offenses: A Randomized Trial in Maryland

November 1999

Kenneth H. Beck, William J. Rauch, Elizabeth A. Baker, Allan F Williams


This randomized experiment measures the effectiveness of a program that instituted breath-alcohol detectors connected to the ignitions of drinking-and-driving offenders for one year. Drivers who had committed two drinking-and-driving offenses were randomly assigned to either the treatment or control group. Those in the treatment group were 64% less likely to commit another offense in the first year.

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Policy Implications

This experiment shows that breath-alcohol detectors connected to ignitions are an effective way of decreasing recidivism among drunk-drivers. However, this effect disappears in the second year, when the alcohol-detectors are no longer present. Therefore, policies may need to find ways to adapt in order to sustain the effect.

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