It’s difficult to tell how a joint or marijuana-laced brownie will affect anyone. And, without reliable standards and testing devices, it’s even more difficult for police to prove that Colorado drivers are impaired by it.

With Legal Pot, Testing Impairment Became Harder

Just as smoking a joint can impair your judgment, police nationwide are having a difficult time judging how deeply cannabis is affecting you while behind the wheel. Ironically, the question “Are you high?” is even more difficult considering that pot is now legal in Colorado — and driving while impaired isn’t.

Laws governing marijuana are changing across America, and in response, so too are the science and policies regarding how high is too high and how soon after smoking is too soon.

Detection has shifted from urine tests to blood tests and, today, saliva samples, as the law shifted its eye from one type of marijuana trace chemical to another, The Denver Post writer David Migoya reported. The nuances make the problem clearly different from alcohol abuse on the road and a critical issue for lawmakers and prosecutors. Since legalization, they’ve been trying to respond to pot’s increased role in traffic fatalities across the state.

Not All Pot Chemicals the Same

Testing for marijuana in a user’s system has always centered on its essential chemical, tetrahydrocannabinol (THC), Migoya reported. The tests focused on the trace chemical called carboxy THC because it shows up in large quantities and accurately indicates that someone previously used marijuana. However, researchers learned that it wasn’t the actual intoxicating chemical in marijuana and could show up as long as one month after use. Other residual varieties of THC, however, are better indicators that someone used pot recently — within a couple of hours — and to some testers is a better indicator that the user is still high.

THC’s Effects Do Not Mimic Alcohol

Just as alcohol and THC give users different highs, they react and break down differently in users’ bodies. It’s widely accepted that drinkers are drunk when they have a 0.08 blood-alcohol content level and may be impaired with a level of 0.05 or more. Some people will avoid the risk of exceeding the limits by simply quitting after two drinks.

But with marijuana or THC, researchers, lawmakers, and users have difficulty creating a benchmark for intoxication, Migoya wrote. Users can experience completely different intoxication levels and durations depending on how they ingested it — smoking it, eating it, and using concentrates — and how much they ingested. Because of the blurry lines, Colorado law requires the state to show that an accused driver had a certain level of THC in his or her body, but also convince a judge or jury that the driver was impaired by it.

A Call for Better Testing Tools

In October 2018, the National Transportation Safety Board directed one of its divisions to give states more guidance on fighting drug-impaired driving and develop standards for portable devices that would let police test drivers during traffic stops, Bloomberg News Ryan Beene and Alan Levin reported. The safety board announced the plans as it unveiled its findings on a 2017 crash in rural Texas that killed 13. The responsible driver was high on marijuana and prescription medication as he drove his pickup into oncoming traffic and crashed into a church bus.

The National Highway Traffic Safety Administration reported to Congress about problems determining how severe pot-impaired driving and the auto accidents they may cause are and questioned the reliability of available tests. It also described conflicting reports about how severely the drug undermines road safety.

Comments given to The Post by Greenwood Village Police Chief John Jackson echoed the federal government’s assessment, saying:

“We’re in the infancy with this, and it’s very much an unknown since we don’t have the data. … We spent 25 or 30 years figuring out where we were are with alcohol, and finally got to breathalyzers. … [Without a test,] you will not convince those who believe it’s safer that it’s not. It becomes so emotional to the point of irrational.”

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