United States Department of Transportation
i
Alcohol Ignition Interlock Use Rates Following Changes in Interlock Legislation
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2020-11-01
[PDF-1.47 MB]
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Edition:Final Report 9/24/2014-9/23/2017
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Abstract:Ignition interlocks are effective at preventing driving under the influence (DUI) of alcohol while installed on vehicles. However, the rate of interlock use is low relative to the numbers of DUI arrests and convictions, even in States that mandate interlock use for all DUI offenders. Accordingly, there is interest in identifying ways to increase interlock use, including by expanding the types of offenses for which an offender is eligible or required to use an interlock. This study examined how changes to interlock law affected interlock use in Florida and West Virginia. Each State had expanded the types of DUI offenses that result in mandatory or voluntary use of an interlock. The study compared the number of new interlock installations, interlocks-in-place (interlocks currently installed), installations as a proportion of those eligible to use interlocks, and lack of use or low use of the vehicles with interlocks, before and after the States modified their laws. The analyses found statistically significant increases in interlock use in both States after changes were made to their interlock laws. The Florida data showed increases of 21.8 percent in all DUI offenders mandated to install; 69 percent in first offenders mandated to install; 122.3 percent more installations overall; and 27.8 percent more installations for first offenders mandated to install. The West Virginia data showed an increase of 242 percent in interlock installations after a 2010 change in the interlock law, and an increase of 60 percent after a 2014 change to interlock law; however, the measure “interlocks-in-place” did not reveal changes, which may be due to limitations in the data used to capture the number of installations and removals. The results showed an increase in interlock installations after changes to DUI law expanded the types of DUI offenses, such as a “high-BAC” offense, that mandate or permit as an alternative sanction, interlock use. This outcome, though not surprising, suggests that previously some offenders avoided enrolling in interlock programs. Results also showed that barriers to interlock use can emerge when the law requires that offenders fulfill obligations unrelated to their DUI charge to qualify for interlocks program, such as paying past fines or child support. Finally, the study highlights the importance of interlock data systems for States to track trends in interlock use and evaluate interlock programs.
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