istock / Jan Priems

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.

Because of the issues with blood tests, several companies are racing to develop a functional breathalyzer. So far, none have delivered the goods. In theory, a pot breathalyzer would be similar to the breathalyzers used to measure blood alcohol content. Proponents argue that breathalyzers are great because they show whether a person has consumed marijuana recently. Skeptics claim that what is in the breath may not be in the brain.

Expect technology and the law to evolve when it comes to testing for stoned driving. Oregon’s current approach to testing is rational in the sense that it does not simply rely on a potentially inaccurate drug test. However, it leaves a great deal of discretion to police, which makes many people uncomfortable. As legalization continues to spread across the country, it is likely some method of testing will win out and there will be more consistency to testing for stoned driving. But that’s probably a few years away.