Alcohol Ignition Interlock Use Rates Following Changes in Interlock Legislation

McKnight, A.S.; Tippetts, AS · 2020 · ROSA P / United States. National Highway Traffic Safety Administration. Office of Behavioral Safety Research

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Summary

This study, conducted by the Pacific Institute for Research and Evaluation for the National Highway Traffic Safety Administration, examines how changes in state legislation affect the use rates of alcohol ignition interlock devices. While interlocks are proven to reduce impaired driving recidivism while installed, usage rates remain low relative to DUI arrests and convictions. The research aimed to determine if expanding eligibility or altering legal mandates could increase interlock adoption, specifically analyzing data from Florida and West Virginia following legislative changes. The researchers employed a quasi-experimental design using archival data from interlock vendors and state agencies. They compared interlock metrics before and after specific legal interventions in each state. The primary measures analyzed included the number of new installations, the number of interlocks currently in place, installations as a proportion of eligible offenders, and "lack-of-use" rates derived from vehicle start logs. In Florida, the study focused on a 2008 law that lowered the blood alcohol concentration (BAC) threshold for mandatory interlock installation for first-time offenders from 0.20 g/dL to 0.15 g/dL. In West Virginia, the analysis covered multiple legislative changes, notably a 2010 law allowing expungement for first-offense offenders who completed interlock programs and a 2014 law permitting offenders to avoid license revocation by installing an interlock. The results indicated statistically significant increases in interlock installations in both states following the legal changes. In Florida, the number of first-time offenders mandated to install interlocks increased by 69%, and actual installations by first-time offenders rose by 27.8%. Overall installations in Florida increased by 122.3%. In West Virginia, autoregressive integrated moving average models showed a 242% increase in installations following the 2010 law and a 60% increase after the 2014 law. However, the measure of "interlocks-in-place" did not show significant changes in either state, likely due to data limitations regarding the synchronization of installation and removal records. Additionally, lack-of-use rates in Florida did not change significantly, while West Virginia saw a 60.3% reduction in lack-of-use following the 2008 law. The study concludes that expanding the types of DUI offenses that mandate or permit interlock use effectively increases installation rates, suggesting that many offenders previously avoided enrollment despite mandates. The findings also highlight that barriers to interlock use emerge when eligibility is tied to unrelated obligations, such as paying past fines or child support. The report emphasizes the importance of robust data systems for states to track trends and evaluate program effectiveness, noting that legislative strategies can successfully overcome offender resistance to interlock installation.

Key finding

Expanding interlock eligibility through legislative changes resulted in statistically significant increases in interlock installations in both Florida and West Virginia.

Methodology

dataset

Provenance

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Topics

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• alcohol detection systems
• dui enforcement