It is, of course, illegal to drive a vehicle while impaired by the effects of marijuana. The continuing problem, however, is: How do you prove that a driver is, in fact, under the influence of marijuana?
Law enforcement currently relies primarily upon the opinions of police officers as to whether a suspect is unable to safely operate a vehicle due to marijuana impairment. The primary tool used to arrive at this opinion is the same as for alcohol impairment: field sobriety tests. These highly subjective roadside "tests", administered and interpreted by a police officer with little training, is coming under increasing scrutiny — as reflected in yesterday’s decision by the Massachusetts Supreme Court:
Court: Roadside Drunken Driving Tests Not Valid for Pot
Boston, MA. Sept 19 – The highest court in Massachusetts has ruled that field sobriety tests typically used in drunken driving cases cannot be used as conclusive evidence that a motorist was operating under the influence of marijuana.
The Supreme Judicial Court on Tuesday said police officers could testify only to their observations about how a person performed during a roadside test.
But they would not be allowed to testify as to whether a person passed or failed such a test or offer their own opinions about whether a driver was too high to drive.
The justices said there is currently no reliable scientific test for marijuana impairment.
Adult use of recreational marijuana is now legal in Massachusetts, though the court noted it’s still illegal to drive while high on pot.
Absent evidence of impairment based upon field sobriety tests, the only other evidence (independent of a police officer’s subjective opinion), is a blood test. This, however, has been proven to be highly unreliable. See, for example, Can DUI Marijuana Be Detected or Measured?, How Much Marijuana Does It Take to Impair Driving? and New Study: Minimal Impairment from Marijuana.
(Thanks to Joe)