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.