The Washington PostDemocracy Dies in Darkness

How just a couple drinks make your odds of a car crash skyrocket

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The National Highway Traffic Safety Administration recently released a pair of reports on drunk and drugged driving. I've already written about how the data show that stoned driving is a lot safer than drunk driving. But one of the reports also quantifies the increase in crash risk as a driver's blood alcohol concentration (BAC) increases, and boy is it something.

In all 50 states, the legal threshold for driving under the influence falls at 0.08% BAC. But as you can see from this chart, the risk of a car crash starts rising at BAC thresholds well below that. At a BAC of 0.05 -- completely street-legal -- your odds of wrecking your car have increased 100 percent versus someone who hasn't drunk at all. At 0.08, your crash odds have roughly tripled.

Depending on your weight and gender, it doesn't take many drinks to reach those BAC thresholds. If you're a 160-pound man, it takes just two drinks in an hour to reach a BAC of 0.05. If you're a 120-pound woman, 2 drinks will land you in 0.08 territory.

For that 160-pound man, five drinks in an hour leads to a BAC of .12 and an elevated crash risk of 682 percent (no, that figure's not missing any decimals).

These numbers underscore the arbitrariness of the 0.08 DUI threshold -- why do we accept a doubled risk of crash at 0.05 BAC, but not a triple risk? And why do we severely punish stoned driving at THC thresholds that correspond to no increased risk of crash at all?