Ethan Siegel and Alex Berezow are right to identify marijuana-impaired driving as a significant national highway safety problem, but no equivalent will ever exist for marijuana or any other drug like the familiar 0.08 BAC for alcohol (“We Need a DUI Test for Marijuana,” op-ed, Aug. 23).
This is because, unlike for alcohol, for other drugs there is no close relationship between tissue levels and impairment. The search for a tissue level that defines impairment for marijuana or other drugs is illusory. Moreover, it is not possible to determine when marijuana was last used because of the drastic differences in the metabolism of edible versus smoked products and because chronic marijuana users show deficits in driving skills after three weeks of abstinence.
There are good ideas available right now. Test all drivers arrested for impairment, not just for alcohol but also for marijuana and other commonly used drugs. Use Administrative License Revocation to immediately remove from the road drug-positive drivers identified as impaired. Use the zero tolerance per se standard for illegal drug use. But don’t delay effective action now on marijuana-impaired driving in the hopes that there will be a blood test for “marijuana intoxication.”