People ages 55 and older may be too dangerous to drive after just a single alcoholic drink, though younger drivers were not affected in a new study from the University of Florida.

Psychologist Sara Jo Nixon says new findings on the safety of driving after moderate alcohol doses may convince policymakers to strengthen impaired driving laws. In the study, she and her colleague Alfredo Sklar tested the driving abilities of 36 study participants ages 25 to 35, which they compared to scores for another three-dozen older people ages 55 to 70.

Although a single drink left all of the study participants well below legal definitions of intoxication, older drivers were deemed too dangerous after just one serving of alcohol. "These simulations have been used a lot in looking at older adults, and they have been used at looking how alcohol affects the driving of younger adults, but no one's ever looked at the combination of aging drivers and alcohol," Sklar said in a statement.

Though much is known about the effects of heavy drinking on driving ability, the research pair says little attention has been paid to the effects of lower doses — a much more common problem in the United States, particularly as baby boomers retire and age.

To establish a baseline, both groups were tested on a virtual course offering a gentle decline down a three-mile stretch of country road with not much opposing traffic. On a simulator with three monitors, covering direct and peripheral vision, everyone from both groups scored well on driving abilities.

However, older drivers scored significantly worse after taking a single drink — when legally sober, the researchers found. To quantify the effects of increasingly minute doses of alcohol, the researchers on a later day tested older drivers with blood alcohol concentrations (BAC) of between 0.04 to 0.065 percent, with both groups below the 0.08 percent standard commonly used in the United States.

Expecting to find both groups of drivers impaired after just one drink, Nixon acknowledged she felt a “bit surprised” to find younger drivers inured to the effects of moderate doses of alcohol. Data from laboratory experiments may not entirely replicate the typical, real-world of driving, she said, attempting to “walk back” the findings.

The same might be said for both age groups studied in the laboratory, however. Still, U.S. states continue to allow motorists to drive with higher BAC limits than other developed countries. Last year, the National Transportation Safety Board recommended that all 50 states lower their drunk driving standards from the common 0.08 percent to 0.05 percent.

Source: Nixon, Sara Jo. Pharmacology. 2014.