Alcohol ignition interlocks are a type of situational prevention measure aimed at reducing drink driving (also known as drunk driving, driving under the influence (DUI), driving while intoxicated (DWI)) and the harm caused by alcohol-related crashes. They are commonly prescribed in sentencing decisions by the Court or Judges, or used as a prerequisite for a driving license reinstatement.
To operate a vehicle with an interlock device, the driver must give a breath specimen with an acceptable blood alcohol concentration (BAC). If the BAC in the specimen is over a certain threshold, the vehicle will not start. Advances in interlock technology in the 1990s added features that made circumvention more difficult.
This narrative summary is based on three systematic reviews: Review 1 (14 studies), Review 2 (15 studies) and Review 3 (6 studies). None of the primary studies were carried out in the UK and although at least one UK bus company uses them as standard in their new coaches it is not clear whether this intervention is available at the present time.
Overall, the evidence suggests that ignition interlocks reduce drink-driving recidivism while the device is installed.
Review 1 estimated that for every 100 alcohol-related traffic violations committed by drivers without alcohol interlocks on their vehicles, an average of 36 violations would be expected among drivers with interlocks. This beneficial effect disappeared when the ignition interlock device was removed.
Descriptive analysis in the three reviews suggest that similar effects were found for drink-driving re-arrest rates (Review 1, 13 studies; Review 2, 9 studies; Review 3, 5 studies). Review 2 provided limited evidence that alcohol-related crashes may also decrease when interlocks are installed in vehicles (based on 3 studies).
The overall evidence is taken from a systematic review covering 14 studies (Review 1). The review was sufficiently systematic that many forms of bias that could influence the study conclusions can be ruled out. However, the meta-analysis in this review was conducted on only one randomised control trial (RCT) study which is problematic. The authors further note that the cohort studied in the RCT could be considered to be highly motivated to change their behaviour and not representative of less motivated offenders, further skewing the effect size. The results of this review should therefore be treated with caution.
The supporting evidence from Reviews 2 and 3 presented descriptive results and is therefore considered weaker.
Little information regarding mechanism is provided in any of the reviews. Review 1 notes that the ignition interlock modifies the offender's habits related to drinking and driving, as it provides immediate feedback on inappropriate alcohol consumption.
There is little evidence to show that the effectiveness of ignition interlocks varies by context. Reviews 1 and 2 found that interlocks are as effective with first-time offenders as they are with repeat offenders.
Moderators suggested (but not tested) were: mandatory vs. voluntary participation (Review 1), whether the ignition interlocks were implemented with other support services (e.g. alcohol rehabilitation programmes) (Reviews 1 and 2), whether judges have discretion in prescribing the intervention (Review 2), the point at which the intervention is offered (after arrest vs. after sentencing) (Review 2), the length of the intervention period (Review 2).
Ignition interlocks are implemented within the context of the sentencing frameworks of the US, Canada, Australia and Sweden (where the primary studies were carried out), and require substantial resources to administer (Review 2). The main challenges to implementation are participation rates, compliance and the durability of the effect -especially once the interlock is removed (Review 1).
Participation rates were low across all the reviewed studies. Even mandatory participation only resulted in 62% of the recruitment of offenders in a sample (Review 1, 1 study). Incentives for using interlocks include reduced insurance premiums, and reducing the time taken to get a license reinstated (Review 1). Other strategies to increase participation rates include increasing the number of offenders eligible for the interlock intervention, and offering alternative sanctions (such as home confinement) (Review 2).
Compliance can be enhanced by implementing interlocks with features which counter circumvention and by collecting data on how the interlock is used (Review 3). Participants should be trained in using the interlock and be required to bring their vehicle to an authorised service centre regularly for maintenance, inspection and downloading of the recorded interlock data (Reviews 1 and 2). These data can be checked for signs of circumvention (Review 2). The negative consequences of failing to participate in the programme should be increased to ensure compliance (Review 2).
All three reviews reported that the beneficial effect of the interlock intervention disappears when it is removed. It therefore has no lasting change on drink driving behaviour. Review 2 reported that using the interlock in conjunction with alcohol rehabilitation programmes appeared to increase the effectiveness of the intervention (1 study).
The review does not mention costs (and/or benefits) and no formal economic analysis is provided. However, the following points are made relating to costs:
Review 1 notes that the cost of installing and maintaining the interlock is borne by the driver.
Review 2 states that the intervention requires substantial administrative resources to lease, install, and monitor the device.
The low participation rates in ignition interlock programmes are problematic and, consequently, the evidence base on the effect on different sub-groups of drink drivers is weak.
The situational crime prevention framework suggests that ignition interlocks might increase the effort needed to commit crime rather than achieve long-lasting behaviour change. This can explain (a) why we do not see contextual variations across different types of participant and (b) why the effect disappears when the ignition interlocks are removed.
Displacement of crime – from one vehicle to another - was not reported, but should be considered a possibility.
Overall, the evidence suggests that ignition interlocks reduce drink-driving recidivism while the device is installed, but this effect disappears when the interlocks are removed. Participation rates were noted to be a problem in all three reviews. The quality of the evidence is weak and further studies are needed to test the mechanism, the context in which the intervention might work, and provide economic analysis of the intervention.
Review 1: Willis C, Lybrand S, Bellamy N. (2004). Alcohol ignition interlock programmes for reducing drink driving recidivism. Cochrane Database of Systematic Reviews, Issue 3. Art. No.: CD004168. DOI: 10.1002/14651858.CD004168.pub2.
Review 2: Elder R W, Voas, R, Beirness, D, Shults, R A, Sleet, D A, Nichols, J L, Compton, R. (2011). Effectiveness of Ignition Interlocks for Preventing Alcohol-Impaired Driving and Alcohol-Related Crashes. American Journal of Preventative Medicine. 40(3): pp. 362-376.
Review 3: Coben, J H & Larkin, G L. (1999). Effectiveness of Ignition Interlock Devices in Reducing Drunk Driving Recidivism. American Journal of Preventative Medicine 16 (1) Supplement 1, Jan 1999, p.81-87.
This narrative was prepared by UCL Jill Dando Institute and was co-funded by the College of Policing and the Economic and Social Research Council (ESRC). ESRC Grant title: 'University Consortium for Evidence-Based Crime Reduction'. Grant Ref: ES/L007223/1.
Uploaded on 19/02/15