It is, of course, against the law to driver under the influence of marijuana (sometimes called "stoned driving"). In most cases, a blood sample will be drawn and analyzed to provide evidence of impariment. And as I've discussed in previous posts, there are nearly insurmountable problems law enforcement and prosecutors have with this. See, for example, Identifying and Proving DUI Marijuana ("Stoned Driving"), Driving + Traces of Marijuana = DUI, How Accurate is Detection and Evidence of Drugged Driving? and DUI Marijuana: Does Marijuana Impair Driving?
Quite simply, it is extremely difficult if not impossible to prove that the presence of given levels of marijuana in the blood proves that the suspect was impaired when driving. First, there is very little agreement on how much marijuana it takes to impair a driver's physical and mental faculties. Second, it is difficult to determine from blood tests what the active levels were at the time of driving. It is a scientific fact that inactive metabolites of marijuana remain in the bloodstream for weeks.
But, of course, there is a simple solution — similar to one created a few years ago which made it easier to convict citizens accused of driving while under the influence of alcohol. Fqced with difficulties in proving alcohol impairment, the various states simply passed so-called "per se" laws — laws which made having .08% of alcohol in the blood while driving a crime. Impairment was no longer an issue to be proven; the crime was simply having the alcohol in your blood. And the conviction rates increased dramatically.
Today, a similar approach is being used by a growing number of states: making the mere presence of marijuana in the blood while driving a crime — regardless of whether it had any effect.
Some courts, however, are beginning to have concerns about this "per se" approach:
Presence of THC Metabolite in Blood Does Not Prove Impaired Driving , Arizona Supreme Court Finds
Phoenix, AZ — Arizonans who smoke marijuana can’t be charged with driving while impaired absent actual evidence they are affected by the drug, the Arizona Supreme Court ruled Tuesday.
The justices rejected arguments by the Maricopa County Attorney’s Office that a motorist whose blood contains a slight amount of a certain metabolite of marijuana can be presumed to be driving illegally because he or she is impaired, saying medical evidence shows that’s not the case.
The ruling most immediately affects the 40,000-plus Arizonans who are legal medical marijuana users. It means they will not be effectively banned from driving, given how long the metabolite, carboxy-THC, remains in the blood.
It also provides legal protection against impaired-driving charges for anyone else who drives and has used marijuana in the last 30 days — legal or otherwise — as well as provides a shield for those who might be visiting from Washington or Colorado, where recreational use of the drug is legal.
Maricopa County Attorney Bill Montgomery said Tuesday’s ruling will result in roads that are less safe. He said if courts will not accept carboxy-THC readings as evidence of impairment, then there is no way of knowing who is really “high” and who is not…
A breath of fresh air in the ongoing hysteria of MADD's "War on Drunk Driving"…
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