Half of all drinkers may be driving over the legal alcohol limit, study finds

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Experts say consumers are underestimating how drunk they really are before getting behind the wheel

Researchers from the University of Cambridge believe many consumers may be driving while drunk and not even realizing it. According to their recent study, about half of all drinkers are not good at gauging how drunk they are. This often causes them to get behind the wheel while exceeding the legal alcohol limit. 

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

Drinking and driving don’t mix

For the study, the researchers had 90 participants involved in a drinking and driving experiment over the course of two days. The participants were in either an experimental or control group and were instructed to drink a combination of beer and wine until their blood alcohol concentration (BAC) reached 0.11%; in the U.S., the legal driving limit is 0.08%. 

To assess how well the participants knew their own bodies, the team tracked their BAC with breathalyzer tests and had them come forward when they believed they reached the legal driving limit. The researchers told participants in the experimental group that when they hit the legal limit, their beverage of choice would be switched – from either beer to wine, or vice versa. 

Ultimately, the participants struggled to accurately assess how drunk they were in both trials of the study. In fact, their ability to estimate their BAC got worse between the first and second days of the experiment. 

During the first day, nearly 40% of the participants had exceeded the legal driving limit when they believed they were just reaching it. By day two, that figure jumped to more than 50% of participants. The researchers believe that awareness is the key to ensuring consumers aren’t driving drunk. Moving forward, they hope more work is done to get drinkers to understand their limits. 

“Drinking and driving is a major risk factor for road traffic accidents,” said Dr. Hensel. “Anything that can be done to reduce these numbers is worth trying. With guidance, our participants were able to improve their judgement. It could be that pop-up stalls set up around drinking establishments that help people understand their breath alcohol concentration might help. 

“Really, the best advice is that if you’re driving, just don’t drink,” he added. “But if you really do feel like a drink, then look into your alcohol tolerance. This differs from one person to the next, depending on your sex, weight, and age, and there are some reliable apps out there that can help guide you.” 

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