Marijuana Legalization and Traffic Deaths: Looking Beyond the Stats

Friday, December 2nd, 2011

Recently, we were puzzled by the Wall Street Journal headline: “Do Medical Marijuana Laws Reduce Highway Deaths?”  The article covered a new study showing a nearly 9 percent decrease in traffic fatalities in states that have legalized medical marijuana.  Not surprisingly, the study authors pointed to possible causes behind this trend: marijuana use may be partially replacing alcohol use in these states, and marijuana users are less inclined to get high in places (like bars or sports events) from which they need to drive home.  But can we really conclude that medical marijuana legalization reduces traffic deaths?  Not likely.  This strikes us as a case in which correlation does not imply causation.

Just because there’s an inverse relationship between two variables—in this case, medical marijuana laws and traffic fatalities—doesn’t mean that one led to the other.  And it certainly doesn’t mean that marijuana does less harm than alcohol when the user gets behind the wheel.  Impaired driving is impaired driving—whether someone drives drunk, high, or medicated.  The statistics are staggering: 18 percent of fatally injured drivers test positive for at least one intoxicant.  We need to focus on prevention and treatment efforts that will help reduce this figure—not on whether one drug may be less pernicious than another.  The message should be clear: Drug use can never make our roads safer.

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