States with laws that mandate ignition interlocks for all drunk driving offenders have reduced drunk driving fatalities by 16%, according to a new study from the Insurance Institute for Highway Safety (IIHS). 

The study authors 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 did not involve impairment. Alcohol impaired was defined as drivers with blood alcohol concentrations (BAC) of 0.08 percent or higher.

The results showed that drunk driving fatalities fell 3% when states required ignition interlock laws for repeat offenders only. Moreover, those states that mandated interlocks for repeat offenders as well as first offenders with high blood alcohol concentrations (BAC) saw an 8% reduction in alcohol-related deaths.

However, study authors attribute the greatest impact — a 16% reduction in impaired driving fatalities — to states that have laws requiring interlocks for all DUI offenders.

If all states adopted all-offender interlock laws, more than 500 additional lives could be saved every year, according to the IIHS.

Presently, 45 states mandate interlocks for at least certain impaired-driving offenders, and 31 states and the District of Columbia have laws that require interlocks after the first offense at 0.08 BAC or higher. On March 26, Idaho became the 31st state when Gov. Butch Otter signed into law legislation that mandates all first-time drunk driving offenders use an interlock for one year.

Drunk driving is the leading killer on U.S. roads, accounting for 10,497 fatalities in 2016 alone.