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There’s No Scientific Basis for Current Marijuana Driving Laws, Study Argues

And fatal road crashes in Washington have doubled since marijuana legalization.

| 3 min read

And fatal road crashes in Washington have doubled since marijuana legalization.

As marijuana continues to become legalized for both medicinal and recreational purposes in the US, it’s critical to establish marijuana driving laws that have a scientific basis — because a new study commissioned by the AAA Foundation for Traffic Safety argues that the current regulations are essentially meaningless.

"There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment in the same manner we do alcohol," said Marshall Doney, AAA's president and CEO, in a media release. "In the case of marijuana, this approach is flawed and not supported by scientific research."

A few states — Colorado, Montana, Nevada, Ohio, Pennsylvania, and Washington — currently rely on a blood-test threshold for THC, which is the chemical in marijuana that makes people high. Similar to when an individual tests over the .08 blood-alcohol content (BAC) limit in drunk driving cases, an individual will automatically be presumed guilty if he or she tests higher than the legal blood-THC threshold.  

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However, this method is extremely flawed, the study argues, because it’s not possible to set a blood-THC threshold test that reliably determines impairment at the time of the incident.

Why? Because regular smokers may have higher levels of THC in their systems even if they aren’t too impaired to drive at the time, while those who don’t smoke often may have low levels of THC in their blood but be unsafe behind the wheel. It’s far more complex than the simple tests allow for, and there’s no science that shows all drivers will become impaired at a specific level of THC in the blood.

The foundation says that some drivers who are unsafe might be going free while others who aren’t too impaired to drive may be wrongfully convicted.

Further, a handful of states, including some where marijuana is legalized for medicinal use, have zero-tolerance laws for driving and marijuana. This means that not only could the presence of THC in a driver’s blood result in a DUI offense, but also the presence of THC metabolites, which can linger in the blood for weeks after use.

Mark A. R. Kleiman, a New York University professor specializing in issues involving drugs and criminal policy, tells the Associated Press that this law makes no sense. "A law against driving with THC in your bloodstream is not a law you can know you are obeying except by never smoking marijuana or never driving.”

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Kleiman says that studies show that driving under the influence of marijuana roughly doubles the risk of a crash, while talking on a hands-free cellphone — which is legal in all states — quadruples the risk. A BAC of .12, which is about the median in drunk driving cases, increases the crash risk by about 15 times, he says.

In fact, driving with "a noisy child in the back of the car" is about as dangerous as using marijuana and driving, Kleiman told AP.

The AAA researchers recommend training police officers with special techniques to determine whether a driver is too impaired by marijuana, like screening for pupil dilation, tongue color, certain behaviors, and more.

The foundation also found that fatal car crashes involving drivers who had recently smoked marijuana doubled in Washington after the state legalized the drug, which raises serious concerns about marijuana and driving, with at least 20 more states considering legalization this year.

"The significant increase in fatal crashes involving marijuana is alarming," Peter Kissinger, President and CEO of the AAA Foundation for Traffic Safety, said in a statement. "Washington serves as an eye-opening case study for what other states may experience with road safety after legalizing the drug."

Now more than ever, it’s clear that there’s a dire need to create new marijuana driving regulations that are supported by science.

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