Andrea Roth


As the marijuana legalization movement advances, states face a jurisprudential dilemma in addressing the burgeoning public health issue of “drugged driving.” Zero-tolerance laws targeting drivers with any illegal drugs in their systems, currently justified under a “jurisprudence of prohibition” based on the blameworthiness of the drug itself, are no longer a good fit due to legalization. Instead, states have attempted to treat marijuana like alcohol by importing drunk driving’s “jurisprudence of dangerousness” through enactment of per se driving under the influence of (DUI) marijuana laws redefining DUI as driving with a certain quantifiable amount of THC, marijuana’s main psychoactive compound, in one’s blood. These laws are legitimate, legislators claim, because they are analogous to per se .08 percent blood-alcohol concentration (BAC) impairment laws. What lawmakers have forgotten, and what legal scholars have largely neglected, is the buried and colorful history of drunk driving’s jurisprudence of dangerousness and the scientific framework for proving the link between specific BACs and crash risk established by the country’s first “traffic czar,” William Haddon Jr. Under this framework — which focuses first and foremost on fatal single-car crashes and case-control studies with a randomly selected control group — the illegitimacy of the new wave of DUI marijuana laws is painfully obvious. In fact, the few single-car crash and case-control studies that have been conducted have found no relationship between THC blood levels and an increased relative crash risk. Properly understood, the history of drunk driving jurisprudence offers what is still the only valid scientific framework for criminalizing chemical impairment.