The logic behind Utah's change is simple: Your odds of getting into a car crash while driving at .05 are dramatically lower than the odds at .08.
Take a look, courtesy of the National Highway Transit Safety Administration:
At a BAC of .08, a driver's odds of getting into a crash are about four times greater than a sober driver's. At .05, however, the crash risk is halved relative to the risk at .08 — although it's worth pointing out that even at .05, your odds of a crash are still double what they'd be if you were completely sober.
Utah was the first state to lower the drunken driving limit from .10 to .08, way back in 1983. Delaware was the last state to do so, in 2004, and only then under threat of losing federal highway funds.
The current shift to .05 in Utah has been opposed by Democrats worried about harm to the state's tourism industry, as well as alcohol industry trade groups like the American Beverage Institute, which characterizes the change as “criminalizing perfectly responsible behavior.”
But “laboratory research shows that most people's critical driving skills are significantly impaired at .05 BAC,” according to a review of the literature by James Fell and Robert Voas of the Pacific Institute for Research and Evaluation.
A separate literature review conducted by Fell and Voas on countries that implemented the lower BAC found “the evidence is consistent and persuasive that fatal and injury crashes involving drinking drivers decrease at least 5—8% and up to 18%.”