ng/mL, and 43 percent had THC concen- trations less than 1ng/mL.5
THC concen-
trations were higher when drivers did not have other drugs detected in their blood. But there is more; THC rapidly clears the bloodstream, but it persists in fat-contain- ing tissues including the brain. Terefore, within minutes aſter smoking marijuana, blood THC concentrations fall rapidly while impairment rises. Blood is difficult to obtain in highway setings, making it likely that many hours will pass between arrest and blood collection. Using the 5 ng/mL per se limit for THC in blood, claiming it as a highway traffic safety standard, gives the appearance of being tough on marijuana- impaired driving, while actually giving a pass to virtually all marijuana smokers. For this reason, it is worse than no standard.
Te details regarding the factors that
make establishing a tissue concentration definition of drug-impaired driving were the subject of a recent article to which readers are referred: Reisfield, G. M., Goldberger, B. A., Gold, M. S., & DuPont, R. L. (2012). Te mirage of impairing drug concentration thresholds: A rationale for zero tolerance per se driving under the influence of drugs laws. Journal of Analytical Toxicology, 36(5), 353-356.
The Alternative to the BAC 0.08 g/dL Equivalent If it is neither possible nor practical to
identify a blood concentration that defines drug impairment, what can be done to iden- tify and reduce drugged driving? Fortunately there are three well-established experiences
that provide useful precedents for developing a more effective drugged driving enforcement policy. Drug testing is at the center of each. First, in the late 1980s, the United States
developed a policy to curb drug-related problems in safety-sensitive positions, includ- ing the aviation, highway, railroad, transit, pipeline, and maritime industries. Tis policy set a zero tolerance standard for any concen- tration of prohibited drugs or drug metabolite in urine, making an exception for drugs that were prescribed for the worker. Under this program, any evidence of recent drug use in a drug test is a violation, whether impairment is observed or not. Under this approach, the fact of the drug’s illegality is crucial; for illegal drug use, the standard is zero. Second, many countries in Western
Europe have confronted the drugged driv-
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