Weed smokers like to say that getting high doesn’t affect how they drive. Now, it appears the federal government is agreeing with them.

According to a new study commissioned by the National Highway Traffic Safety Administration, people who smoke marijuana have a minimally higher risk of crashing than those who stay sober. During a 20-month study of 10,858 drivers in Virginia Beach, researchers working 24/7 compared drug and alcohol readings from people involved in crashes against similar people (at the same time of day and location) who kept their cars intact. The main takeaway: When factoring age, sex, and race, there was no “significant increased risk of crash involvement” due to marijuana use.

Excluding those demographics, NHTSA said stoners had a 25-percent higher risk of crashing but at the same time attributed that increase to a greater representation of younger, predominantly male drivers who already top actuarial spreadsheets for loss and damages. Weird as it seems, the actual measured risk of THC-registered drivers, at five percent higher than sober drivers, dropped to zero when those drivers had also consumed alcohol. (You may have heard some uproar in 2013 about random police checkpoints asking drivers for anonymous blood, saliva, and breath samples. That was part of a separate survey, and right now, the marijuana study is the only one of its kind to correlate marijuana impairment and vehicle accidents in such an exacting way.)

When it came to just alcohol, the outlook predictably got worse. At a blood-alcohol content of 0.05—interestingly, the lower limit suggested by the NTSB and which we support—drivers were twice as likely to have an accident than someone who hadn’t touched any booze. At the legal 0.08 nationwide limit, that risk climbed to fourfold; at 0.12, it was nearly eight times higher.

There are several caveats that NHTSA fully admits. Unlike alcohol, THC concentrations in the blood don’t necessarily equate to intoxication at that moment (the mind-altering substance can be detected for days, if not weeks, afterward). Tolerance, metabolism, and various other degrees to which marijuana affects different people are also difficult to establish in studies like these. The 2682 car crashes the study investigated, 15 of which involved fatalities, were “less severe” and meant to mimic the majority of accidents that occur each day and week across the U.S. Had the researchers focused only on more severe and deadly crashes, marijuana (and other prescription and illegal drugs tested) might pose a higher risk. There’s also the little issue of the lack of any uniform test or scientific determination of a driver’s true impairment. No one, not even authorities in states like Colorado, has come up with a simple solution. NHTSA says it simply doesn’t know as much about pot as it does about alcohol.

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