Since Colorado voters legalized pot in 2012, prohibition supporters have warned that recreational marijuana will lead to a scourge of “drugged drivers” on the state’s roads. They often point out that when the state legalized medical marijuana in 2001, there was a surge in drivers found to have smoked pot. They also point to studies showing that in other states that have legalized pot for medical purposes, we’ve seen an increase in the number of drivers testing positive for the drug who were involved in fatal car accidents. The anti-pot group SAM recently pointed out that even before the first legal pot store opened in Washington state, the number of drivers in that state testing positive for pot jumped by a third.
The problem with these criticisms is that we can test only for the presence of marijuana metabolites, not for inebriation. Metabolites can linger in the body for days after the drug’s effects wear off — sometimes even for weeks. Because we all metabolize drugs differently (and at different times and under different conditions), all that a positive test tells us is that the driver has smoked pot at some point in the past few days or weeks.
It makes sense that loosening restrictions on pot would result in a higher percentage of drivers involved in fatal traffic accidents having smoked the drug at some point over the past few days or weeks. You’d also expect to find that a higher percentage of churchgoers, good Samaritans and soup kitchen volunteers would have pot in their system. You’d expect a similar result among any large sampling of people. This doesn’t necessarily mean that marijuana caused or was even a contributing factor to accidents, traffic violations or fatalities.
This isn’t an argument that pot wasn’t a factor in at least some of those accidents, either. But that’s precisely the point. A post-accident test for marijuana metabolites doesn’t tell us much at all about whether pot contributed to the accident.
Since the new Colorado law took effect in January, the “drugged driver” panic has only intensified. I’ve already written about one dubious example, in which the Colorado Highway Patrol and some local and national media perpetuated a story that a driver was high on pot when he slammed into a couple of police cars parked on an interstate exit ramp. While the driver did have some pot in his system, his blood-alcohol level was off the charts and was far more likely the cause of the accident. In my colleague Marc Fisher’s recent dispatch from Colorado, law enforcement officials there and in bordering states warned that they’re seeing more drugged drivers. Congress recently held hearings on the matter, complete with dire predictions such as “We are going to have a lot more people stoned on the highway and there will be consequences,” from Rep. John Mica (R-Fla.). Some have called for a zero tolerance policy — if you’re driving with any trace of pot in your system, you’re guilty of a DWI. That would effectively ban anyone who smokes pot from driving for up to a couple of weeks after their last joint, including people who legitimately use the drug for medical reasons.
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