"We need to treat DUID as important [an offense] as murder, rape, and child molestation." -- John Bobo, Director, National Traffic Law Center. "Enforcement and Prosecution of Drugged Driving Laws," speech given February 23, 2004
Mere Presence is Enough. No Impairment Required
Most states still have "effect based" laws that forbid the operation of a motor vehicle if a person is either "under the influence" or sometimes "incapable of driving safely" due to the use of a drug. Virtually nobody objects to such laws. However "per se" laws prohibit the operation of a motor vehicle if an individual has any amount of a drug or its metabolite in his/her system. This approach is based on convenience - not science. It is, in the words of one of its chief proponents, "divorced from impairment."
Espcially Problemmatic for Marijuana
In the case of marijuana, these laws are particularly troublesome. Marijuana's primary metabolite, THC-COOH, is inactive (i.e., no intoxicating effects whatsoever), but is detectable in urine for days and weeks after use. Consequently, under a "zero tolerance" law someone who smoked a joint in Amsterdam on Monday could be arrested the following Friday in Detroit and charged with driving under the influence even though he or she is clearly no longer impaired.