Pop quiz: At what blood alcohol level does it become unsafe to drive? If you answered 0.08%, you are wrong—possibly dead wrong. Yes, it is legal for a person age 21 or older to drive provided that his/her blood alcohol content (aka blood alcohol concentration or BAC) is below 0.08%…but the legal limit has surprisingly little connection to the actual safe limit.

Why? Because according to a large-scale new study, your likelihood of causing a fatal car crash rises significantly even when your BAC means that you’re only very slightly buzzed. The proof is in the numbers…


Traffic accidents have consistently been the leading cause of fatal injuries in the US. More than one-third of all crash deaths involve a driver who was legally drunk…and that figure would be significantly higher if it also included drivers who were impaired by alcohol yet whose BAC was below 0.08%. The fact is, that 0.08% cutoff is arbitrary—in most European countries, the legal limit is 0.05%, and even that level is too high for safety, it now appears.

New study: To look at the proportion of accidents caused by drivers who had been drinking, researchers used data from the National Highway Traffic Safety Administration (NHTSA). This government agency maintains detailed information on every police-reported fatal traffic accident in the country. The database includes information on each driver’s BAC…plus driving-related factors that contributed to the crash, such as running a red light, making an improper turn or driving on the wrong side of the road. These driving-related factors are determined by the police officers investigating the crash.

The researchers calculated—for each increment of BAC down to a hundredth of a percent—the percentage of two-car fatal accidents in which one driver was solely and officially blamed for the crash. Only driver-related factors were considered, not weather or roadway conditions, which, of course, would be exactly the same for both drivers involved in the accident. More than 570,000 fatal accidents were included in the analysis, many of which involved collisions between a sober driver and a drinking driver.


Here’s a shocker: “Minimally buzzed” drivers—those with a BAC of just 0.01%—were 46% more likely to be solely responsible for a fatal crash than the sober drivers they collided with.

To put this in perspective, consider that a 125-pound woman who drinks one small (four-ounce) glass of wine over the course of an hour is likely to have a BAC of about 0.02%. This BAC is double the minimally buzzed level discussed above that contributed so significantly to fatality blame. Explanation: Even at a very low BAC, judgment is affected…there’s a decline in the ability to visually track a moving object…and there’s a decline in the ability to perform two tasks simultaneously (such as talking and paying attention to road conditions).

Now consider the case of a 185-pound man who consumes three typical beers over the course of two hours. His BAC is likely to be slightly above 0.04%. The researchers found that drivers with BACs at this level were about twice as likely to be solely to blame for a fatal crash as the sober drivers with whom they collided.

No magic line: The researchers also determined that there was no magic line or “threshold effect”—no sudden transition between a blameless and a blameworthy BAC. Instead, there was a direct linear relationship between increased BAC and increased likelihood of blame. The higher the BAC, the more probable it was that the drinking driver caused the fatal crash. This may seem intuitive and obvious. What’s not obvious, then, is why drivers who are below the 0.08% threshold often are given a pass, legally speaking, when it comes to the alcohol—even though their decision to drive after drinking caused the deaths of others. The public, the police and judges consider the 0.08% BAC to be a sharp, definitive, meaningful boundary…which it is legally, but not in actuality. This needs to change! The law should reflect what the official accident investigators are seeing, the researchers said—and I agree.

Before you imbibe: Spend some time studying a blood alcohol calculator so you get a general idea of how drinking affects your BAC. Many factors contribute to alcohol’s effects, including your age, gender and size, how quickly the alcohol is consumed and whether you have anything to eat before drinking. Also consider the fact that, once you stop drinking, it takes about 40 minutes for your BAC to drop by one-hundredth of one percentage point. So if you drink to the point where your BAC reaches 0.07% and then you stop, it will be four hours before your BAC falls to 0.01%…and even then, you will still be at increased risk for causing an accident that proves fatal to you or to someone else.

Bottom line: The only truly safe course of action is not to get behind the wheel after drinking at all.

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