Efforts to develop an accurate and easy-to-use roadside test for marijuana intoxication are understandable and worthwhile. Breathalyzers used to test blood-alcohol levels make for an obvious comparison.
The problem is that while Colorado’s legalization of recreational marijuana envisioned treating pot like alcohol, in many respects, it is not like alcohol. So far at least, there is no quick and accurate field test for marijuana intoxication and no agreed-upon standard for what blood levels of its active ingredient mean.
As the Herald reported Tuesday, several companies are working to develop a device that could be used roadside to test drivers for marijuana impairment. None, however, has succeeded so far.
With that, the best measure of whether someone is too stoned to drive remains the judgement of a well-trained cop. And given the nature of marijuana that could be true for some time.
That does not mean that law enforcement is without options or that marijuana users can drive around with impunity. There are many different intoxicating drugs available today – legal and illegal – and police officers are trained to recognize impairment in all forms. It simply means the quick and easy roadside example of Breathalyzers is not yet applicable to marijuana.
Alcohol is unique in how it is metabolized, how it affects drivers and how different blood-alcohol levels are reflected in behavior are all well understood and thoroughly tested. That is not the case with marijuana.
For starters, evidence of marijuana use lingers in the body for weeks – long after the user is actually high. An effective test, therefore, has to measure only the psychoactive ingredient of marijuana, called delta 9 tetrahydrocannabinol, or THC. There are lab tests for THC, just not a roadside version.
What that means is that a police officer has to make an initial determination as to whether a driver is impaired and, if so, run the lab test later. (As with alcohol, the driver can refuse the test, but will then lose his driver’s license.)
In 2013, the Colorado Legislature established a blood-level limit for marijuana at 5 nanograms of THC per milliliter of blood. That, too, is controversial, with critics claiming the limit is arbitrary. Of course, all limits are to some extent arbitrary, but in this case the critics have a point. There is little hard data connecting THC dosage directly to increased risk as there is with alcohol. And even otherwise authoritative sources disagree.
The Colorado Department of Transportation, for example, says, “Marijuana affects reaction time, short-term memory, hand-eye coordination, concentration and perception of time and distance.” Its statistics show that 5.7 percent of the drivers involved in fatal crashes in 2013 tested positive for cannabis. On the other hand, the National Highway Traffic Safety Administration finds no evidence that using marijuana leads to a higher risk of being in a traffic crash.
With that kind of contradictory thinking around pot’s affects, perhaps the idea of a clear and simple test – one that would yield a number like those used to measure blood alcohol – is unrealistic. The idea of such a standard is appealing. Below the line a driver is good; above it, a driver is in trouble. It seems just and has the air of scientific certainty.
But it may not be any such thing. Especially in the age of ubiquitous video, with marijuana, it may well be that the best gauge of whether a driver is impaired is still a well-trained cop.
