Since Colorado voters legalised pot in 2012, prohibition supporters have warned that recreational marijuana will lead to a scourge of “drugged divers” 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.