With the push to legalize marijuana, states want to assure the public that roads will be safe. They face a perplexing question, reports McClatchy Newspapers: How stoned is too stoned to drive? “The answer is: Pretty damned stoned is not as dangerous as drunk,” said Mark Kleiman, professor of public policy at the University of California, Los Angeles, Washington state's top pot consultant. He said Washington state’s law is far too strict and could lead to convictions of sober drivers, with many not even knowing whether they're abiding by the law.
With no conclusive research, states are all over the map as they try to assess intoxication by measuring blood levels of THC, the main ingredient in marijuana. There's no easy way to do it, with marijuana stored in fat cells and detectable in blood long after it's smoked or consumed, for days or weeks, depending on individual tolerance and level of use. Washington and Colorado, the only two states to legalize marijuana fully, have set a limit of five nanograms of active THC per milliliter of blood. In Washington state, legalization proponents included the language in the ballot initiative approved by voters in 2012. “It appealed to the voters, but it's nonsense _ it's not a good measure of whether somebody's impaired or not,” Kleiman said. “The fact that legislatures will not do their job on this means we go through the cockamamie initiative process; it's a lousy way to write legislation.”