A new Colorado State University analysis finds that after Utah slashed its legal blood-alcohol limit for drivers to 0.05 grams per deciliter, the state saw steeper drops in alcohol-involved fatal crashes than its neighbors. Researchers used a quasi-experimental approach that compared counties over several years to tease out how much of the change could be traced to the law itself.
What the research measured
The study, published in the American Journal of Preventive Medicine, pulled from national Fatality Analysis Reporting System (FARS) data covering 2013 through 2023. Using a difference-in-differences design, the team compared Utah with six bordering states to estimate how fatal crash rates shifted after the law took effect.
The authors report difference-in-differences estimates roughly between −0.67 and −1.17 and say the biggest reductions showed up in crashes involving drivers with any detectable alcohol in their system (BAC ≥ 0.01). Those numbers point to a policy-level decline in alcohol-involved fatalities, according to the journal.
Researchers' conclusions
Lead author Kaigang Li of Colorado State University told KUNC that "The findings definitely indicate that a lower BAC limit can be an effective public health strategy for reducing impaired driving, deaths, and improving roadway safety."
To keep things apples-to-apples, the team lined up county-level crash data from Utah alongside counties in Arizona, Colorado, Idaho, Nevada, New Mexico, and Wyoming. By controlling for regional trends, they found that the drops were concentrated in alcohol-involved crashes rather than in overall fatal wrecks alone.
Utah's law and enforcement
Utah became the first and, so far, only state in the country to lower its per se blood-alcohol limit from 0.08 to 0.05 when HB155 kicked in on December 30, 2018. The Utah Highway Safety Office has said the change was designed to cut impaired driving and save lives.
Utah Highway Safety Office materials explain that the 0.05 rule is woven into a broader impaired-driving strategy that relies on education campaigns and enforcement to support the lower limit. The Colorado State University findings also made it to TV, with CBS News Colorado airing a short segment and posting the video online.
What it means going forward
The authors and public-health advocates say a 0.05 per se limit is not a magic switch. They argue that it works best when paired with consistent enforcement, ongoing public education, and related prevention programs if states want to keep fatal crashes trending downward.
The research was funded by the National Institute on Alcohol Abuse and Alcoholism, and the journal's publisher later summarized the findings in a press release, according to Elsevier.
