Tommy Chong makes no secret of his endorsement of being stoned in almost any situation. Even driving.

"Everybody's worried about driving when you're stoned. Noooo. You're not going to hurt anybody going five miles an hour,” he says. “But you do get paranoid at the wrong times. One time I got pulled over by a caution light. I sat there for a long time, man."

There's never been a clearer explanation of why you shouldn't drive when you're intoxicated — on anything.

But now data show that even when the buzz fades, if you use marijuana regularly, you're still an on-road hazard to yourself and others.

Researchers from MacLean Hospital's Cognitive and Clinical Neuroimaging Core and the Marijuana Investigations for Neuroscientific Discovery (MIND) program published a study in the journal Drug and Alcohol Dependence that looked at chronic users' driving skills.

Those were people who had used in five or more of the past seven days, reported using at least 1,500 times in their life, and then abstained for at least 12 hours before participating in the study. 

The results clearly showed that chronic users have more accidents, drive faster, and drive through more red lights than nonusers.Folks who started smoking weed regularly as teens have the worst driving skills.