A 2013 study by economists at the University of Colorado Denver and Montana State University revealed that so-called “per se” drugged driving laws have no discernible impact on traffic fatalities.
Per se laws set specific thresholds for controlled substances, above which drivers are automatically considered impaired. They are, in other words, based on a number rather than on actual impairment. Such limits are much harder to apply to a substance like marijuana than to alcohol, since individual responses and tolerances to cannabis vary so widely.
These laws criminalize some cannabis-using drivers hours, days, or even weeks after they’ve last used the herb, even if the person’s driving ability was never impaired in the least. THC is fat soluble, and since the endocannabinoids are naturally present anyway, the body loves it and holds onto it as long as it can. It may stay in regular, heavy users’ systems for weeks after they’ve last used pot; I once tested positive 49 days after my last use.
Since 1990, at least 12 states have passed “zero-tolerance” drugged driving laws, making it illegal to drive with any detectable levels of a controlled substance in the bloodstream. At least four more have passed similar laws specifying non-zero — but still absurdly low — limits for marijuana or its metabolites.
“These laws are intended to make the job of prosecuting drugged drivers easier,” said Daniel Rees, professor of economics at the University of Colorado Denver who coauthored the study with D. Mark Anderson, assistant professor of economics at Montana State University, reports David Kelly at Phys.org. “In states without these laws, prosecutors must rely on field sobriety tests or evidence that a motorist was driving erratically in order to prove impairment.”
Now, while basing a driving while impaired ticket on actual impairment seems to make the most sense, drivers in at least 16 states have more to worry about than whether or not their actually impaired — they have to worry about having smoked weed days and in some case weeks before.
The infamous Office of National Drug Control Policy (ONDCP, the office overseen by the “drug czar”) has announced a goal of reducing drugged driving by 10 percent. In an effort to achieve this goal, the ONDCP is encouraging all 50 states to prohibit driving with detectable levels of a controlled substance in the system. Zero tolerance, in other words.Although the new zero tolerance laws almost certainly make prosecuting and convicting people easier, no study had examined their effectiveness until this one.
Using state data from the Fatality Analysis Reporting System (FARS) for 1990-2010, Anderson and Rees looked at the link between adopting controlled substance thresholds for drivers and traffic fatalities. They found no discernible relationship at all, and concluded that there’s no evidence that these limits reduce traffic deaths.
“Our study is particularly timely given that Washington voters recently passed Initiative 502, which legalized the recreational use of marijuana but prohibited driving with THC levels equal to, or greater than, five nanograms per milliliter of blood,” Anderson said. “Setting a THC standard for drivers may, in the future, be viewed by voters as a necessary complement to legalizing marijuana for recreational or medicinal use.”
Although the percentage of drivers testing positive for cannabis and other controlled substances is highest during the night and on weekends, they found no evidence in the FARS data that these laws — which, remember, have been adopted by 16 states — led to any reduction in traffic fatalities at any time.
“As currently implemented, these laws have no discernible impact on traffic fatalities,” Rees said.
The study is available at: http://www.iza.org/en/webcontent/publications/papers/viewAbstract?dp_id=7048.