As marijuana use grows more accepted in the United States, accidents caused by stoned drivers are climbing rapidly, reports the LA Times. And with no medical standards like blood-alcohol levels, law enforcement officials are struggling to determine impairment under pot. More than 16% of nighttime drivers have drugs in their system, half of them marijuana, according to the most recent survey National Highway Traffic Safety Administration. Another study said that non-alcohol-related driving fatalities were up 55% over the decade before 2010.
"A lot of effort has gone into the study of drugged driving and marijuana, because that is the most prevalent drug, but we are not nearly to the point where we are with alcohol," said the National Highway Traffic Safety Administration's impaired-driving director. "We don't know what level of marijuana impairs a driver." But not everyone thinks that impairment standards can be so clear cut. "Everybody wants a magic number, because that makes it easy," said one toxicologist, however, "a law that says above a certain level you are impaired is not scientifically supportable."