Dear Pot Lawyer,
How can the police gauge stoned driving?
MEASURING cannabis intoxication is tough and there is no generally accepted method. In Oregon, we do not use blood tests or the mythical cannabis breathalyzer. Instead, it is up to the officer to demand a field sobriety test upon suspicion of impairment (big pupils, sloppy speech, tongue color, etc.). If the driver fails, he or she can be brought to the police station, where more tests await and a prosecutor decides whether to bring drugged driving charges.
As states continue to legalize cannabis, driving while stoned is an issue that gets lots of play. That is because weed use and heavy machinery are not a great fit, testing methods are controversial, and there is no science showing that drivers become impaired at a certain level of THC in the blood. A daily cannabis user may not be impaired despite relatively high blood levels, whereas a lightweight may be all over the road with lower THC levels. One recent study found driving stoned about as distracting as driving with a noisy child in the back of a car. It also found that driving stoned roughly doubles the risk of a crash.
With respect to testing methodology, blood tests are unreliable. THC may remain in a person’s blood for days or weeks after consumption; or, it may not yet be detectable, even if the person has recently smoked copious amounts of weed. There is usually a gap of a few hours from the arrest to blood collection as well, due to warrant and transport issues. These facts have not stopped Washington, Colorado, and several other states from using THC blood levels to test for cannabis impairment. In addition, nine states still have zero-tolerance laws for stoned driving, which make not only the presence of THC in a driver’s blood illegal, but also its metabolites. That seems pretty dumb.