Brian Palmer discovers that it’s an open and shut case, for Slate:
A new study suggests that legalizing medical marijuana reduces traffic fatalities. The authors noted that legalizing marijuana reduces alcohol consumption, and people are more wary of driving high than drunk. Which drug is actually more dangerous on the road?
Alcohol, and it’s not even close. It’s hard to directly compare alcohol and marijuana, because driving impairment depends on dosage and the two drugs tend to affect different skills. (Pot makes drivers worse at mindless tasks like staying in a lane, while alcohol undermines behaviors that require more attention like yielding to pedestrians or taking note of stop signs.) Nevertheless, Yale psychiatrist Richard Sewell reviewed the academic literature on driving while intoxicated in a 2009 article, and found that alcohol is significantly more dangerous. Real-world data from auto accidents indicate that a drunk driver is approximately 10 times more likely to cause a fatal accident than a stoned driver. In most studies, smoking one-third of a joint or less has virtually no impact on a driver’s performance. A couple of studies even suggest that pot smokers are less likely to cause an accident than sober drivers.
It’s a little surprising that THC has such a small effect on driving. In experiments testing the skills required for driving—coordination, visual tracking, and reaction time—rather than driving itself, subjects under the influence of pot fare significantly worse than sober people. But when you put them behind the wheel of a driving simulator, tokers perform okay. Those who have taken in a moderate dose of the drug show minimal impairment, and very experienced smokers show almost no deficit at all. (Interestingly, habitual stoners are also better at driving drunk than ordinary people.)…
[continues at Slate]