How do you know if you're too stoned to drive? It is important to note that states legalizing cannabis have not seen an increase in impaired driving or crashes. And driving under the influence of alcohol remains a much bigger and more dangerous threat. But the epidemic of impaired and distracted driving in America is well documented and those many crashes, injuries, and deaths undoubtedly include some instances of stoned driving.
The problem with addressing stoned driving has always been that the only way to test for it is to conduct a blood draw and measure the driver's THC level. But THC levels often decrease in the time between being stopped and the time the blood is drawn, meaning that many who drive stoned cannot be caught.
Washington was sufficiently concerned about stoned driving that when it legalized recreational cannabis, it set a level of 5 nanograms of THC per milliliter of blood, or above, as constituting impaired driving. But another problem with addressing stoned driving is that nobody is really sure what level of THC would indicate impaired driving.
Cannabis is unlike alcohol in that frequent users develop a level of habituation that eliminates many of the perceptual and motor impairments that result from using cannabis. In other words, many stoners can still fly down the ski slope just fine. But alcoholics, not so much.
But that is really all we know, and there are many questions left to be answered about how cannabis affects humans, including the important issue of when humans are too impaired to drive. Those questions are not being answered thanks to the federal policy effectively banning all research on cannabis. That seems poised to change, but don't hold your breath.
In the meantime, researchers are working to develop a breathalyzer that can detect THC levels, just as current breathalyzers detect alcohol levels. Hound Labs Inc, which is based in Oakland, California, in collaboration with scientists at UC Berkeley, will begin trials of such a device in 2016. Researchers at Washington State University are also working on such a breathalyzer.
The goal will be to create a single device that police can use to test for both alcohol and cannabis impairment in a single "blow." Although that would certainly seem to help address any cannabis-impaired driving, the problem remains that there remains no scientifically valid way to determine what level of THC would constitute impairment.
Perhaps more problematic, even if an impairment level could be set, such a standard would not account for cannabis habituation in regular users. So will the cannabis breathalyzer become a lifesaver? Or a tool for continued harassment of cannabis users? This issue is just another reason why it is critical to lift the federal ban on cannabis research.