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Status Report, Vol. 35, No. 1 | January 15, 2000 Subscribe

Ignition interlocks reduce rearrest rates of alcohol offenders

Keeping drivers with repeated alcohol offenses from continuing to drink and drive has been a long-term problem for law enforcement authorities. Ignition interlock devices that prevent drinking drivers from starting their cars may offer a solution.

In a recent Institute-sponsored study of repeat offenders, ignition interlocks reduced the risk of alcohol traffic violations by 64 percent during the first year they were required (see "Ignition interlocks help curb violations among repeat DUI/DWI offenders," May 10, 1997).

"It's encouraging that such large reductions in recidivism were found in a population with serious multiple alcohol offenses," says Kenneth Beck of the University of Maryland, the study's lead author. Now results are available for a second year of the study, during which interlocks were removed.

Ignition interlocks have been around for some time, but this study is the first to scientifically evaluate their effectiveness using random assignment methods to ensure comparability of the groups. The results are especially important given the few effective alternatives available.

Multiple alcohol offenders in Maryland who were approved by a medical board to regain their driver's licenses were randomly assigned to either ignition interlocks or standard treatment regimens. Only 2.4 percent of the 698 people assigned to use the interlocks were rearrested for alcohol violations during the first year the devices were required. This compares with 6.7 percent of the 689 who received the standard treatment.

Repeat offenders have to blow into a device like this before starting their cars. Interlocks are an effective means to reduce rearrest among multiple offenders. (Photo courtesy of LifeSafer)

Ignition interlock device

In the second year, when interlocks could be — and in most cases were — removed, 3.5 percent of the remaining interlock group participants and 2.6 percent of the controls were rearrested, a difference that isn't statistically significant. During the combined two years of the study, 5.9 percent of the interlock group and 9.1 percent of the controls had been cited for at least one alcohol traffic violation, a statistically significant difference.

"An ignition interlock license restriction program is an effective means to reduce rearrest among multiple offenders, although the positive effects were limited to the first year, when the interlock restriction was in force," Beck says. "Consideration should be given to extending the interlock requirement beyond one year."

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