Marijuana legalization not linked to traffic accidents, study shows

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Marijuana, and all its related and derivative products, represent thorny legal territory for the trucking industry, but despite decades of claims of "reefer madness," its legalization appears to have no impact on traffic accidents, according to a new report from academics at the University of Arkansas, Iowa State University, and the University of Tennessee. 

The paper, entitled "Marijuana Legalization and Truck Safety: Does the Pineapple Express Damage More Pineapples?," sets out to assess "whether legalization has affected the crash rates of heavy trucks" and promptly concludes that "legalization does not increase average crash rates." 

The paper's authors analyzed heavy-truck crash data for years 2005-2019, so the results haven't been skewed by the pandemic, which saw many fewer drivers on the road but more severe crashes and more speeding among many drivers, particularly those who share the road with professionals. Researchers then basically looked at heavy truck crashes before and after states enacted a form of legalization or otherwise liberalized rules around marijuana consumption. They found some states faired better and some worse after legalization, but the trend overall pointed down. Vermont and Washington, for instance, saw "large crash reductions," while Nevada on the other hand experienced a big increase, according to the study. 

The paper does not suggest that marijuana use represents a safe choice for commercial vehicle operators, and indeed cites other research that shows THC, the principal psychoactive component of the plant, "diminishes drivers’ ability to perform key tasks such as maintaining the correct road position..., quickly reacting to unexpected events ..., and focusing on the task at hand."

The study cites past research finding that people high on marijuana "tend to compensate for their impairment by slowing down and driving more cautiously," but that "experienced marijuana users show virtually no functional impairment while driving under the influence of THC alone."

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In the end, the study's authors chalk up the road safety improvements in states with marijuana legalization to its impact on alcohol abuse, which data shows really does seem to drive increased crash numbers. In essence, when marijuana becomes legal, many people, including the most dangerous cohort of drivers (young men), reduce their problem drinking behaviors and increase their marijuana consumption. 

Trucking, testing, and personal freedoms

Andrew Balthrop, a research associate at the University of Arkansas and one of the study's authors, said the main implication of the research in his view is for drug testing. 

"There's a big push on the part of some carriers to have hair testing with the idea that it makes testing a little more rigorous with a look-back window that’s longer," Balthrop said. The current standard of urine testing is "really good at picking up marijuana, but hair testing gets more other stuff."

A recent study from the large-carrier-comprised Trucking Alliance and the University of Central Arkansas in January used hair drug testing results from Trucking Alliance member carriers to suggest that drivers actually use cocaine more than marijuana, and that hair testing would essentially double the number of drivers disqualified for drug use

With that question in mind, Balthrop and his team set about answering the question: "How big of a problem in the industry is marijuana actually?"

Balthrop also seemed to have in mind the personal choice and freedoms of commercial vehicle drivers, noting he could think of another regulation in such murky territory where "what you're doing while you're not at work" is nonetheless restricted from an activity "legal for residents of that state," he said. Drivers can drink alcohol when not on the job because alcohol is legal; as long as they're not intoxicated or impaired on the job, they're free to indulge. But marijuana can show up on urine tests up to a month after consumption and remains federally illegal and completely out of bounds for commercial haulers. 

Yet it's also legal in many states, as noted. As of 2019, the last year of data the study looked at, most states had enacted some form of marijuana legalization or regulatory liberalization.  

Many contend that until there's a kind of "marijuana breathalyzer" to determine if a driver is presently intoxicated, these two substances will still be treated differently in the eyes of federal regulators. 

Professional drivers know those rules, a possible explanation Balthrop put forward for the disconnect between legalization and heavy truck crashes. Simply put: The vast majority of drivers don't use marijuana. Yet complicating that picture has been the rise of marijuana derivatives and relatives, like CBD, as treatments for common ailments like aches and pains and alternatives to more addictive and harmful opioids. 

[Related: Can truck drivers use CBD? All you need to know about cannabis, hemp, testing and the clearinghouse]

Looking forward, Balthrop hopes to further this line of research by looking at data from drivers who did fail drug tests for marijuana. "Did they have more hard braking?" he asked. "Did they look less safe on the road?" 

Additionally, getting some idea of the impact of marijuana legalization on road safety allows researchers to do some comparing and contrasting to other regulations. Balthrop said the ELD mandate, which his research has suggested "increased speeding and unsafe driving behaviors" (also corresponding with an uptick in crashes), makes for an interesting comparison. 

Kinetic energy of a moving object increases exponentially with velocity, making "speeders a lot more dangerous" the faster they go, said Balthrop. Increases in crash severity, and perhaps frequency, follow as a result. If marijuana use in fact does result in slower driving on the whole, "there's some interesting patterns like that which warrant more information," he said.