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Many drinkers fuzzy about when they’ve reached drunk driving limit: study

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North Rhine-Westphalia, Germany — Up to half of individuals whose breath alcohol concentration is over the legal limit to operate a vehicle may overestimate their ability to drive, which could trigger “devastating consequences,” according to a recent study out of England and Germany.

Researchers at Witten/Herdecke University and the University of Cambridge analyzed 90 students in Germany across a two-day experiment, splitting them into two groups: a study group and a control group. Both groups consumed either beer or wine or both until they reached a maximum breath alcohol concentration of 0.11% – exceeding the drunk driving limit in Germany (0.05%) and Great Britain (0.08%).

In the study group, the participants were told at the start that when they reached a breath alcohol concentration of 0.05%, they would be switched from beer to wine or vice versa. However, they weren’t told that the percentage was the legal limit for drunk driving. The researchers tracked the students’ breath alcohol concentration via breathalyzer tests, prompting them to estimate their percentage each time it was measured. The students were asked to come forward when they thought they reached the legal driving limit.

The researchers found that, on the first day, 39% of the participants who felt they reached the legal driving limit had actually exceeded it. On the second day, that percentage increased to 53.


“In countries with legal alcohol limits, it’s usually the driver who makes a judgment about how much they’ve drunk and how fit they are to drive,” said Kai Hensel, lead study author and researcher in the Department of Pediatrics at both universities. “But as we’ve shown, we are not always good at making this judgment. As many as 1 in 2 people in our study underestimated how drunk they were – and this can have devastating consequences.”

In the United States, about 28 people die in crashes related to drunk driving each day, the National Highway Traffic Safety Administration says.

The study was published online Dec. 7 in the Harm Reduction Journal.

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