Guide to community preventive servicesEffectiveness of Ignition Interlocks for Preventing Alcohol-Impaired Driving and Alcohol-Related Crashes: A Community Guide Systematic Review
Introduction
Drivers convicted of driving while impaired (DWI) present a high risk to other highway users. Hedlund and Fell1 found that offenders convicted of DWI are 4.1 times more likely to be involved in a fatal crash while intoxicated by alcohol than are average licensed drivers. Further, 35% to 40% of all fatally injured drinking drivers are estimated to have had at least one prior DWI offense.2, 3 For the first two thirds of the 20th century, the traditional penalties assessed for a DWI conviction were jail, fines, and license suspension. Of these, license suspension has provided the strongest and most consistent evidence of effectiveness in reducing recidivism.4, 5, 6 Nonetheless, both self-reports7 and covert surveillance8 of suspended DWI offenders indicate that many of these drivers continue to drive without licenses or insurance, and that they often continue to do so even after becoming eligible for license reinstatement.9
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Use of Vehicle Sanctions to Reduce Illicit Driving
Given the evidence that suspension alone does not prevent DWI offenders from driving illicitly, state legislatures have enacted various measures that keep impaired-driving offenders from accessing their vehicles, such as vehicle impoundment and immobilization laws10, 11, 12 and vehicle forfeiture laws.13 Although there is evidence that such actions reduce recidivism, they may have potential adverse effects on innocent family members, and therefore have not been widely adopted for a broad range
History of Interlock Development and Use
The first efforts to develop devices to prevent vehicle operation by intoxicated drivers grew out of human performance research. From this work, some prototype devices, such as a “Quick Key” unit that tested the driver's reaction time, were developed for vehicles.14 However, the large variation in human performance resulted in a substantial number of false-positive signals. Subsequent systems were designed to assess intoxication more directly, using a dashboard-mounted breathalyzer device that
Types of Interlock Programs and Their Influence on Interlock Use
One of the most important limiting factors for the public health impact of interlock programs is the relatively small number of offenders who participate in such programs. Despite the continuing growth of interlock use, only a small fraction of the approximately 1.4 million people arrested for DWI annually in the U.S. use them. This apparently low usage rate is partly due to the failure to convict some of the arrested offenders, and it also reflects the policy in most states of confining their
Goals of This Review
One of the primary research issues of interest to the review development team was the degree to which the installation of interlocks in offenders' vehicles reduces alcohol-impaired driving in comparison to alternative sanctions (primarily license suspension). Because this question was addressed thoroughly by a recent systematic review conducted for the Cochrane Collaboration,27 the previous work was not replicated. The current review builds on the earlier Cochrane review by incorporating more
Methods
This review was conceptualized and conducted by a systematic review development team consisting of subject matter experts in traffic safety and systematic review methodology, under the oversight of the independent, nonfederal Task Force on Community Preventive Services (the Task Force) and using the methods of the Guide to Community Preventive Services (Community Guide). Community Guide methods for conducting systematic reviews and linking evidence to effectiveness are described in print
Results. Part I. Intervention and Study Characteristics
Appendix A presents the key intervention and study characteristics for the studies included in this review,21, 23, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43 as well as summaries of their findings. Although several program characteristics varied widely across studies (e.g., the type of program), all or most programs shared several key characteristics. They generally
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were applied to offenders who are at high risk of recidivism, either due to multiple offences or, for first-time
Results from the studies in the Cochrane review
The Cochrane review27 identified 11 studies that evaluated the effects of either the opportunity to have an interlock installed29, 30 or of actual interlock installation31, 32, 33, 34, 35, 36, 37, 38, 39 on re-arrest rates for alcohol-impaired driving.
The first study29 of the effects of the opportunity to have an interlock installed found that randomization to an interlock program through which 64% of eligible offenders' vehicles had interlocks installed was associated with a 64% relative
Applicability
One important issue to consider in any systematic review is the potential applicability of the results to situations in which the intervention is likely to be implemented in the future. The studies included in this review primarily evaluated interlock programs that (1) were directed to “hardcore” drinking drivers, either repeat offenders or first-time offenders who had high BACs at arrest (usually >0.15 g/dL), and (2) enrolled a relatively small subset of all DWI offenders. In contrast, to
Other Benefits and Harms
The primary goal of this review was to evaluate the effectiveness of ignition interlock programs for reducing alcohol-impaired driving and alcohol-related crashes among people who have been arrested or convicted for alcohol-impaired driving (i.e., the specific deterrence of further alcohol-impaired driving). These programs potentially have either beneficial or harmful effects on the general deterrence of alcohol-impaired driving in the broader population (e.g., by heightening or lessening the
Economic Efficiency
Ignition interlock programs have several associated costs (e.g., program administration; leasing, installing, and monitoring the device; auto insurance) and benefits (e.g., increased mobility for the offender, reduced alcohol-impaired driving) that may be important considerations for people making decisions about the structure of interlock programs and for offenders making decisions about participating in them. However, no studies of the costs or economic efficiency of ignition interlock
Barriers to Intervention Implementation
Few barriers exist to the implementation of ignition interlock programs themselves, and 47 U.S. states have such programs. However, there are important barriers to devising interlock programs so that they enroll a sufficient number of offenders to achieve the greatest public health impact. One important barrier to full uptake of ignition interlocks among eligible offenders relates to the lack of strong incentives for participation in interlock programs. There is almost always an explicit or
Conclusion
Based on the results of the studies identified in the Cochrane review and those of the more recent studies identified in this review, there is strong evidence that interlocks are effective in reducing re-arrest rates while they are installed in offenders' vehicles. The limited available evidence from three studies suggests that alcohol-related crashes decrease while interlocks are installed in vehicles. However, the potential for interlock programs to reduce alcohol-impaired driving and
Discussion
Although there is often an expectation that all DWI countermeasure programs, including ignition interlock programs, will have a lasting impact on the drinking–driving behavior of offenders, recidivism rates remain at about 25% to 30%. As a temporary form of incapacitation imposed for a fixed period of time, interlock programs are able to reduce recidivism dramatically while the interlock is in place. However, the evidence indicates that it is unrealistic to expect that the device will have
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Names and affiliations of Task Force members are available at www.thecommunityguide.org/about/task-force-members.html.