The Washington State Patrol is having a problem with cannabis users who get behind the wheel now that legalization has occurred in that state. Toxicologist Brian Capron says that, “A third of our [impaired] drivers in the state of Washington are testing positive for marijuana. Obviously legalization started in 2012, so we have had a sharp increase since then.” Capron assesses blood samples from roughly 13,000 drivers yearly.

The biggest challenge with identifying impaired drivers is that simply having THC in one’s system doesn’t necessarily mean they are actually impaired while on the road. There is no standardized roadside test for cannabis right now, although the breathalyzer technology is being tested and further developed.

The method that is used in Washington and Colorado currently is to ask for a voluntary blood test or go to a judge who would then order the test be taken, after an arrest has been made. Since going to a judge can take a few hours, the police are looking to get a roadside breathalyzer available for quicker action.

Currently both states use a legal limit of five nanograms of THC per milliliter as the point where a driver is legally considered impaired. There is no hard science to show that this level actually proves impairment, according to Capron, “An individual may be over five and not exhibiting any sign of impairment, and that’s why the five is somewhat troublesome. That five hasn’t been shown by science to be that one level where everyone is impaired.”

Other factors that can’t be measured by law enforcement are tolerances built up by regular cannabis users, as well as what kind of strain that the person used. The distinction between the uplifting, energetic feelings associated with sativa and the mellowness of indica strains are not acknowledged by law enforcement, even though it could play a big part in how impaired a driver actually is.

Footnote(s)