A significant body of research clearly demonstrates that alcohol interlocks reduce recidivism among both first time and repeat offenders while the interlock is installed in the vehicle. During the period of interlock installation (i.e., while the device is installed in the vehicle), alcohol interlock users have lower total recidivism compared to non-users. These results are consistent in the United States and Canada.

The use of alcohol interlocks for DWI offenders has historically been low and inconsistent. This is due, in part, to the reluctance of judges to impose alcohol interlocks as a sanction. This reluctance is often a function of familiarity with flaws of early devices and insufficient availability of knowledge of these devices and their effectiveness. Low installation rates are also due in part to the resistance of offenders to install these devices and the ability of licensing agencies to ensure installation when the device is mandated. Programs with better monitoring practices have higher rates of installation.

There are many factors that contribute to judges’ tendencies to not order alcohol interlocks as part of a sentence, including technological effectiveness of the device, lack of information about how to use the device in sentencing, the amount of effort required to monitor compliance with the program, and the fact that the device may be cost prohibitive for a minority of offenders. It has also been expressed that the alcohol interlock device appears too harsh for first offenders and too lenient for repeat offenders. Historical and personal experiences among judges in relation to the sentencing of offenders may be inconsistent with scientific findings and can influence decision-making.

Historically, a problem has emerged surrounding the majority of unlicensed drivers ordered to install an alcohol interlock who continue to drive without installing the device. Many studies conducted over the past two decades estimate that between 25-75% of suspended or revoked drivers continue to drive. Offenders seek to avoid installing the alcohol interlock because the device is accompanied by inconvenience (installation, interval breath tests while driving, servicing of device) and feelings of embarrassment. In order to remedy low participation and compliance rates, methods must be employed to appeal to the offender’s simple cost-benefit evaluations which would either make the use of the interlock more attractive or make the alternative more unpleasant.

Early interlock devices were relatively easy to circumvent or bypass. Offenders were able to circumvent the device by having someone else provide a breath sample or resorting to push starting the vehicle to bypass the alcohol interlock. During the first several weeks, non-compliance is evident by tampering, with failed breath samples and attempting to electronically disengage the device. Research indicates that tampering and circumvention rates decrease over time, perhaps as offenders become more accustomed to the device and gain an understanding of the difficulty and futility of trying to bypass this sophisticated technology. Research has also found that many offenders are surprised to discover that alcohol consumption in the late evening can still result in a failure reading on the alcohol interlock the following morning, which is a valid measure and not a system malfunction as many of them believe.

Research suggests that a high number of blood alcohol concentration (BAC) fail readings from the alcohol interlock data recording device, particularly in excess of .02, is predictive of the likelihood of DWI recidivism. Researchers have also determined that the presence of elevated BAC tests during early morning hours can assist in predicting future DWI offenses. The presence of two or more elevated BAC test results during the morning hours further bolsters the predictive model regarding the likelihood of future DWI offenses. Prediction of repeat offenses has been associated with a profile of drivers who are both multiple offenders and who have more than a few failed breath tests with elevated BACs.

DWI offenders and other participants in alcohol interlock programs report that there are several benefits to having an alcohol interlock installed on their vehicle(s) including the fact that the alcohol interlock forced them to take responsibility and make other plans prior to drinking to prevent them from driving afterwards. The major reported benefit of the alcohol interlock was the guardian function which made it virtually impossible for the offender to commit another DWI offense. While offenders clearly note the benefits of alcohol interlock installation, there are two types of concerns that are usually raised: concerns regarding social aspects such as the embarrassment, stigma, and frustration of providing a breath sample, and technical challenges such as the perceived long warm-up time, invalid samples, and the frequency of re-tests. Family members are also affected by the installation of the alcohol interlock (often in single vehicle families) and have reported issues of mistrust, social embarrassment, and stigma which resulted in a stressful family situation. Offenders with alcohol interlocks require family support in order to comply with the alcohol interlock program and the overall rehabilitation process.

Alcohol interlocks serve as a nexus between criminal justice sanctions and substance abuse treatment by effectively restricting an offender’s driving privileges while giving the offender the opportunity to learn how their alcohol consumption impacts behavior. Alcohol interlocks were never intended as a treatment for alcohol problems and are unlikely to permanently change offender behavior. In order to reduce the likelihood of recidivism once the interlock has been removed, there is a need to incorporate interlocks into a more comprehensive rehabilitation program that deals effectively with the problems that underlie DWI behavior for those who require it.

Many studies demonstrate that alcohol interlocks have a beneficial impact on recidivism as long as the device is installed in the vehicle. Specifically, existing studies converge at the finding that once the device is removed, recidivism rates return to levels comparable to rates of those who did not have an alcohol interlock installed. However, more recent research has revealed that recidivism rates for those offenders who participated in interlock programs remains lower than that of offenders who did not have the device installed (see: Marques et al. 2010; Elder et al. 2011; Rauch et al. 2011; Zador et al. 2011). For example, the Rauch study (2011) found that those offenders who participated in the interlock program had a 36% reduction in DWI recidivism during the two-year intervention and a 26% reduction in DWI recidivism during the two-year post-intervention period. This translated into an overall reduction in recidivism of 32% over the four-year study.

According to cost-benefit analysis produced by the European Road Safety Observatory (2006), findings demonstrated that some of the most cost-effective measures that contribute to the largest reductions in the number of fatalities are new motor vehicle safety features. The report cites a Norwegian study which notes that installing alcohol interlocks in the vehicles of all impaired drivers would have an estimated cost savings of $8.75 for each $1.00 of cost incurred.

Recent increases in the number of interlock installations demonstrate progress. Nationally, the number of interlocks installed in the United States increased from 304,600 in 2013 to 314,714 in 2014 (Roth 2014). While such an increase is promising, it still represents a small percentage (23%) of all offenders arrested for impaired driving annually (1,400,000). Certain states, such as New Mexico, have made considerable gains in increasing installation rates through judicial education, mandatory sentencing, and by presenting offenders with less attractive alternatives such as house arrest. As a result, the installation rate has increased to 49% (Marques et al. 2010).

The limitations of existing research can be organized according to control groups and selection bias. Most of the difficulties surrounding control groups involve the inability and lack of resources to select a control group equivalent to the interlock group, such as control groups of license-suspended impaired drivers. In order to create an appropriate control group, a population of previously convicted impaired drivers would be randomly split into two groups: one receiving the alcohol interlock and the other one not receiving it (see: Raub et al. 2003). Studies involving voluntary participants may have a selection bias effect, which means that there are some differences in these participants who volunteer to participate compared to other eligible offenders which can affect the results. While this limitation is a difficult obstacle to overcome, the differences in experimental and control groups could be addressed in future studies with good planning.

There are five broad areas of future research which require further attention: optimal structure for alcohol interlock programs, interaction between alcohol interlocks and treatment, process evaluations of alcohol interlock programs, and outcome evaluations of alcohol interlock programs. These five areas generally concentrate on how a program is delivered, the monitoring of outcomes for those who receive an interlock and treatment versus those that do not, how the delivery of programs can be improved, and what options exist for improving outcomes to increase effectiveness.

Last updated September 27, 2021