The US government is analyzing data from what it claims is the biggest study on how pot affects how you drive. The participants in the study at the University of Iowa vaporized marijuana (smoke-free campus!), drank, both, or had a placebo and took the wheel of a driving simulator.
"When it comes to cannabis, it's a lot trickier than when it comes to alcohol," says Colorado State Trooper JJ Wolff. "I can't tell you if one joint is going to make you high to the point where you can't drive. That's a really hard question to answer at this point. … "The safest thing to do right now: If you are going to drink any amount, don't drive. And if you are going to consume any amount of cannabis, don't drive."
"Feds test how stoned is too stoned to drive" (USA Today)