Laws requiring all impaired-driving offenders to install alcohol interlocks reduce the number of impaired drivers in fatal crashes by 16%, a new study by the Insurance Institute for Highway Safety (IIHS) has found. If all states without such laws adopted them, more than 500 additional lives could be saved each year, according to the IIHS.

Alcohol interlocks are in-vehicle breath-testing units that require a blood alcohol concentration (BAC) below a certain level, typically somewhere between 0.02% and 0.04%, before the vehicle can be started.

Prevalence of impaired driving

More than a quarter of U.S. crash deaths occur in crashes in which at least one driver has a BAC of 0.08% or higher. The prevalence of impaired driving in fatal crashes has changed little in the past two decades, and interlock laws are one of the few recent policy innovations that have made a difference, the IIHS said.

Forty-five states require interlocks for at least certain impaired-driving offenders. Twenty-eight states, the District of Columbia, and four California counties have some type of interlock requirement that applies to first-time offenders.

Purpose is to reduce recidivism

The IIHS pointed out that even when they are mandated for first offenders, interlocks come into play only after a DUI arrest, so their direct purpose is to reduce recidivism. Like other types of sanctions, however, they may act as a deterrent for those who have not yet committed a first offense if they are well-publicized. Either way, the IIHS added, the overarching goal is to reduce alcohol-impaired driving and the deaths and injuries that result, and the new study shows they have succeeded.

“We looked at the number of alcohol-impaired passenger vehicle drivers involved in fatal crashes over time and compared them with the number of drivers in fatal crashes that didn't involve impairment,” said Eric Teoh, IIHS senior statistician and the paper's lead author. “We found that state laws mandating interlocks for all DUI offenders reduced the number of drivers in fatal crashes with BACs of 0.08% or higher by 16% compared with no interlock law.”

2016: 10,497 deaths involving drivers with BAC of 0.08% or higher

In 2016, the latest year for which fatal crash data are available, 10,497 people died in crashes involving drivers with a BAC of 0.08% or higher. Of those, 8,853 involved impaired passenger-vehicle drivers. At that time, the number of states with first-offender laws was 25. Had all states had all-offender interlock requirements in place, 543 of those deaths would have been prevented, Teoh calculated.

For the purposes of the analysis, Teoh and his co-authors grouped together two types of all-offender interlock laws: those that require all offenders, including first-time offenders, to install interlocks in order to have their license reinstated and those that only require it to drive during a post-conviction suspension. The analysis controlled for factors besides interlock laws that could affect crashes.

Laws that required interlocks for repeat offenders only cut the number of drivers with BACs of 0.08% by 3% compared with no interlock law, and that effect was not statistically significant, the study showed. Laws that required them for both repeat offenders and offenders with high BACs provided an 8% benefit.

'Compelling body of evidence'

The executive director of the Governors Highway Safety Association, Jonathan Adkins, commenting on the IIHS study, said, “This new study adds to a compelling body of evidence that [ignition interlock devices (“IIDs”)] are among the most effective drunk driving countermeasures available. Required IID use can deter both initial drunk driving offenses and recidivism. While in use, IIDs also ensure offenders can get needed support and treatment while remaining mobile to work and care for family members. GHSA encourages all states to adopt laws mandating IID use for all offenders.”

Adkins added that, “[d]espite some successes in reducing drunk driving, the problem remains both substantial and consistent. As a nation, we need to be doing more to address this fundamental traffic safety challenge, and IID use is at the top of the list of proven strategies.

Steven A. Meyerowitz, Esq., is the director of FC&S Legal, the editor-in-chief of the Insurance Coverage Law Report, and the founder and president of Meyerowitz Communications Inc. Email him at smeyerowitz@meyerowitzcommunications.com.

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