A survey of teens and parents earlier this year found a disturbing misinformation trend. Fully 33 percent of teens reported believing that, where marijuana is legal for recreational use, driving while high is also legal. Over 20 percent said that driving while high is common among their friends. Parents were only slightly less likely to be misinformed. Twenty-seven percent believed driving while high was legal in recreational use states, and 14 percent said it was common behavior among their friends.
Over the past decade, the tide on marijuana seemed to turn. Over half of U.S. states, including Arizona, have legalized the drug for at least medical purposes. Eight states and the District of Columbia have decriminalized it for recreational use.
For alcohol, the 0.08 standard is nationwide for ordinary drivers. If you have 0.08 blood alcohol or higher, there's pretty good scientific proof that you're under the influence. When it comes to marijuana's psychoactive component THC, however, it's not so clear. The majority of studies have indeed found that THC can impair your ability to drive, but there just isn't much evidence that the impairment is very substantial.