If all American states adopted laws requiring impaired driving offenders to install alcohol interlocks, more than 500 additional lives could be saved each year, according to the Insurance Institute for Highway Safety (IIHS).

Such laws reduce the number of fatal crashes involving impaired drivers by 16 percent, according to the IIHS’s new study.

“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 study’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 percent or higher by 16 percent compared with no interlock law.”

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 percent, before the vehicle can be started.

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

Forty-five states currently 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.