SWOV Catalogus


Washington state’s alcohol ignition interlock law : effects on recidivism among first-time DUI offenders.
20120576 ST [electronic version only]
McCartt, A.T. Leaf, W.A. Farmer, C.M. & Eichelberger, A.H.
Arlington, VA, Insurance Institute for Highway Safety IIHS, 2012, 42 p., 17 ref.

Samenvatting More than half of U.S. states require some DUI offenders to install ignition interlocks on their vehicles for a certain period of time if they want to drive. Increasingly states are strengthening these laws to apply to all offenders, including first-time offenders. The current study evaluated two changes in Washington state’s interlock law: moving the issuance of interlock orders from the courts to the Department of Licensing in July 2003, and extending the interlock requirement to cover all convicted offenders, including first-time offenders with blood alcohol concentrations (BACs) lower than 0.15 percent (?first simple DUI offenders?), in June 2004. The primary focus was whether or not these law changes affected rates of recidivism among first-time DUI offenders. Trends in the types of convictions resulting from a DUI arrest, rates of interlock orders and installations, and rates of recidivism were examined, using data extracted from driver license records. The main focus was first-time convictions (simple, high-BAC, and test refusal DUI; deferred prosecution; or alcohol-related negligent driving) stemming from arrests on DUI charges occurring during January 1999-June 2006. Regression analyses examined the effects on rates of recidivism of the law changes and of interlock installation rates. Possible general deterrent effects of the law changes on alcohol-impaired driving were examined by comparing trends in single-vehicle nighttime (9 p.m.-6 a.m.) police-reported crashes and fatal crashes in Washington with trends in California and Oregon. Throughout the study period, about three-quarters of DUI offenses were first offenses. Simple DUI convictions and alcohol-related negligent driving convictions each accounted for about 30-40 percent of first DUI-related offenses. After interlocks were required for simple DUIs in 2004, the proportion of simple DUI convictions trended somewhat downward, while the proportion of alcohol-related negligent driving convictions continued a slow, long-term upward trend. The interlock installation rate among first simple DUI offenders increased dramatically as a result of the 2004 law change, going from less than 5 percent before the law change to about one-third after; increases in installation rates were observed among other first DUI offenders as well. Extending the interlock requirement to first simple DUI convictions was estimated to have lowered the cumulative rate of recidivism during the 2 years following arrest by about 12 percent among people with such convictions (e.g., from an expected 10.6 percent without the law change to 9.3 percent among offenders arrested in the second quarter of 2006, the last part of the study period) and by about 11 percent (from an expected 10.2 to 9.1 percent) among all first-time DUI offenders. There was an estimated 0.06 percentage point decrease in the 2-year cumulative recidivism rate for each percentage point increase in the proportion of first simple DUI offenders who installed interlocks. If the interlock installation rate had been 100 percent rather than 34 percent for first simple DUI offenders arrested in the second quarter of 2006, and if the linear relationship between the recidivism rate and the rate of interlock installations continued, the 2-year cumulative recidivism rate could have been reduced from 9.3 to 5.3 percent. Similarly, if the interlock installation rate had been 100 percent rather than 24 percent for all first DUI offenders arrested in the second quarter of 2006, their 2-year cumulative recidivism rate could have been reduced from 9.1 to 3.2 percent. Although interlock installation rates increased somewhat after moving responsibility for issuing interlock orders to the Department of Licensing in 2003, that action did not significantly affect recidivism rates, perhaps due to the short follow-up period before the second law change. The 2004 law change was associated with a 4.8 percent reduction in the risk of single-vehicle nighttime crashes in Washington, but the change was not significant given the variability in the data. A smaller and likewise non-significant reduction in the risk of single-vehicle nighttime fatal crashes was estimated. It is concluded that extending an interlock requirement to all first-time DUI convictions reduces recidivism among the cohort of affected offenders, even with relatively low interlock use rates, and additional gains are likely to be achievable with higher use rates. Jurisdictions should seek ways to increase installation rates among offenders required to install interlocks and should re-consider policies that allow reducing DUI charges to other traffic offenses that do not have an interlock requirement. (Author/publisher)
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