Pot prohibitionists commonly warn that legalizing marijuana will result in more traffic fatalities as the number of stoned drivers on the highways multiplies. But as I explain in my latest Forbes column, documenting marijuana's role in car crashes is a lot harder than the prohibitionists seem to think. Here is how the column starts:
Last year, during a congressional hearing on the threat posed by stoned drivers, a representative of the National Highway Traffic Safety Administration (NHTSA) was asked how many crash fatalities are caused by marijuana each year. "That's difficult to say," replied Jeff Michael, NHTSA's associate administrator for research and program development. "We don't have a precise estimate." The most he was willing to affirm was that the number is "probably not" zero.
Michael knows something that grandstanding politicians and anti-pot activists either do not understand or refuse to acknowledge: Although experiments show that marijuana impairs driving ability, the effects are not nearly as dramatic as those seen with alcohol, and measuring the real-world consequences has proven very difficult, as demonstrated by a landmark study that NHTSA released last Friday. In "the first large-scale [crash risk] study in the United States to include drugs other than alcohol," NHTSA found that, once the data were adjusted for confounding variables, cannabis consumption was not associated with an increased probability of getting into an accident.
Some news outlets accurately reported that result, and some did not, apparently because some reporters actually read the study, while others were content to skim NHTSA's press release. Such carelessness misleads policy makers who are grappling with the issue of how to determine when people are too stoned to drive. It also aids pot prohibitionists, who cite the prospect of more blood on the highways as an important reason to resist legalization.