Since the legalization of recreational marijuana here in Colorado, driving high has been a major safety concern. Everyone wants their roads to be safe, and considering that drunk drivers are involved in a quarter of fatal accidents, preventing the intoxicated from driving is extremely important.

But how does one define impairment from pot? How can you tell whether or not someone is too high to drive?

The fact is, studies regarding the actual impairment of pot smokers are often conflicted and remain inconclusive. Moreover, a safe and fair standard of measuring how stoned someone actually is continues to evade scientists and law enforcement alike.

Tetrahydrocannabinol (commonly abbreviated as THC), the psychoactive ingredient in marijuana, is limited to five nanograms per milliliter of blood for Colorado drivers. While this is a great starting point, what everyone needs to realize is marijuana and alcohol are not the same substance, and probably shouldn’t be treated like they are. Five nanograms of THC is going to have totally different behavioral effects on people of different tolerance levels. A couple puffs from a joint isn’t going to affect Snoop Dogg, but it might send Attorney General Jeff Sessions into a red-eyed whirlwind.

A 0.08 BAC (blood-alcohol content) works great as a legal limit for drunk driving because, even accounting for variances in tolerance, alcohol effects everyone pretty much the same way. In addition, alcohol is one of the only drugs to completely pass through the blood brain barrier (BBB).  This means that the concentration of alcohol in the blood or breath is an accurate representation of what’s in the brain.

But here’s the thing: THC and most other drugs don’t work like that, making accurate levels of “high-ness”, or impairment, really hard to measure. THC can remain in the body for days — even weeks — after use, which is why testing blood, urine, or saliva isn’t practical when assessing if someone is currently impaired.

As if this issue wasn’t already complicated enough, there are thousands of strains of marijuana, all which can be smoked, vaporized, put in an edible, or turned into a concentrate. They all have different levels of THC, and unlike alcohol, using an exact amount is almost impossible. Even the differences between using a sativa or an indica, the two main types of marijuana plant, can be dramatic. Although most strains today are a hybrid of the two, sativas induce a ‘head-high’ while indicas produce more of a relaxing, body-high.

On the more optimistic side, according to a study done by the National Center for Biotechnology Information, “most marijuana-intoxicated drivers show only modest impairments on actual road tests,” and “experienced users show almost no functional impairment.” In contrast to alcohol users, high drivers tend to drive slower, follow further behind, and become more conscientious of traffic rules.

That doesn’t mean that driving all “stoney-boloney” is okay.

In fact, until more research is done on the actual impairment-effect of marijuana and how to measure it, enthusiasts should be even more careful when getting behind the wheel. We want our roads to be free of unnecessary danger, but we also don’t want smokers who are fine to drive to be punished unjustly. In the past, there have likely been a lot of unfair convictions due to a blood or urine test, which could be picking up THC particles from days prior.

Unfortunately, we may never find a perfect way to measure weed-impairment.

Luckily, an Oakland, CA based company, HoundLabs, is working diligently developing and testing a marijuana breathalyzer. The company values safety and fairness, and is attempting to create a product that can not only measure the amount of THC in the body, but how recently it got there. The product will double as an alcohol breathalyzer, and will reportedly pick up THC particles from smoke and edibles.

Currently, they’re working to make their devices more rugged and sturdy for law enforcement officers.

Still, the use of these devices is pretty controversial because the exact relationship between THC and actual impairment still can’t be quantified. On the plus side, they are far less invasive than blood and saliva tests and will at least limit a portion of unfair arrests.

We are still in the baby steps of understanding marijuana and the effects it has on health, society, and vehicular-impairment, but new research is taking place every day.

Until we know more: puff, puff, park.

How do you feel about driving while stoned?  Let us know in both the anonymous poll and the (non-anonymous) comment section below.