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Legal marijuana may lower rate of truck accidents, new research says

It's the first study on marijuana legalization and big-rig crashes

Recreational legalization of marijuana reduced truck crashes by 11%, according to a new study. (Jim Allen/FreightWaves)

A whopping two-thirds of Americans told Pew in 2019 they believe legal marijuana should be the norm — up from 16% in 1989. 

Public opinion has quickly embraced cannabis, which research suggests is far less harmful than controlled substances like heroin or cocaine and legal ones like alcohol and tobacco.

America’s $800 billion trucking industry isn’t matching that shift in public opinion. In fact, it’s taking the complete opposite approach. In January 2020, the Federal Motor Carrier Safety Administration launched the drug and alcohol clearinghouse. Major industry groups, such as the American Trucking Associations, pushed for its creation

The clearinghouse lists all commercial drivers who have failed a drug or alcohol test. Drivers can clear their names from the clearinghouse if they follow a return-to-duty process. The clearinghouse is aimed at ensuring truck drivers who have violated drug or alcohol rules can’t simply jump from job to job and, in turn, increase safety on the road.

It’s unclear how beneficial the law has been to safety, but it has diligently removed plenty of drivers. From January 2020 to April 2022, around 124,000 drivers have been booted from commercial trucking due to failed drug tests. Around 31,000 have followed the return-to-duty procedure and are back on the road.

The vast majority of violations haven’t involved highly addictive and harmful drugs such as opioids, amphetamines, methamphetamine or cocaine, but rather marijuana. More than 74,000 truckers who tested positive for marijuana have been removed from commercial driving since January 2020. (Some of those drivers may have tested positive for other drugs as well.)


The majority of truck drivers removed from the road as of May 1, 2022, tested positive for marijuana. (Graphic courtesy of Federal Motor Carrier Safety Administration)

A new study suggests this focus on kicking out pot-smoking drivers isn’t all that wise. A group of researchers from the University of Tennessee, University of Arkansas and Iowa State University found that recreational marijuana legalization actually reduced heavy truck accidents by 11% in the eight states studied. Six of the eight saw a decrease in truck accidents, while two saw increases. (Note that this is a preprint, meaning it hasn’t undergone peer review yet.)

I recently participated in a Zoom call with two of the researchers: Iowa State assistant professor Jonathan Phares and University of Arkansas communications specialist Ronald James Gordon. 

“We’re not saying definitively that legalization will reduce trucking accidents, but there is some evidence that legalization across the board doesn’t necessarily increase accidents,” Phares said. “There are reasons why accidents could decrease as a result of legalization.”

If subsequent research or peer review confirms this research, the academics involved suggested lawmakers revise the Department of Transportation’s zero-tolerance policy on off-duty marijuana use for truck drivers. 

The researchers studied truck crash statistics from 2005-19 in eight states with legal, recreational marijuana. Six saw decreases in crashes, while two saw increases. Overall, crashes declined by 11%. Here’s a table summarizing those effects:

STATEEFFECT OF LEGALIZATION
California-3.20%
Colorado-18.30%
Massachusetts-18.00%
Maine4.18%
Nevada25.60%
Oregon-3.70%
Vermont-21.50%
Washington-20.10%
Recreational marijuana legalization may decrease truck crashes.

Medical marijuana legalization did not increase crashes, according to the May research. The researchers found “limited evidence of a slight reduction in crashes” following the legalization of medical cannabis. 

The researchers didn’t have a solid explanation for why legal marijuana reduced crashes, but they offered some theories:

  • Those who would normally drink alcohol may have switched to marijuana. Research suggests that driving while high is far less likely to cause a fatal accident than driving while drunk. (Of course, being sober is the safest way to get behind the wheel.)
  • Marijuana is usually consumed at home, not at a bar or restaurant. 

While overall crashes reduced, some states did see an increase in marijuana use. To understand this, the researchers compared Vermont, which saw the largest decrease in crashes, to Nevada, which saw the largest increase. Phares and Gordon provided the following theories:

  • Vermont has far less tourism than Nevada, meaning more people unfamiliar with the state’s roadways are traveling. Travelers are also more likely to be using marijuana outside of the home — particularly those visiting, say, Las Vegas. 
  • Vermont is also more densely populated than Nevada. Longer stretches of roads provide more opportunity for crashes. 

Some of the researchers’ findings seem to contrast with other studies on legal marijuana and driving. A 2021 study from Boston University, for example, found fatal car crashes involving alcohol have not decreased over the past two decades. However, cannabis-involved fatal accidents have doubled, and fatal accidents involving both cannabis and alcohol use have more than doubled. So-called “poly-impaired” crashes have become a concern in states such as Colorado, where law enforcement says impaired driving has contributed to a marked increase in traffic fatalities.

Other inquiries into marijuana and driving suggest legalized marijuana may increase the overall rate of accidents but not necessarily the likelihood of fatal crashes. 

What zero-tolerance marijuana policies mean for trucking

Marijuana is legal for medical use in 37 states and fully legal in 19. It remains a federally-banned substance. Cannabidiol, more commonly called CBD, is federally legal. Truck drivers who live in states where cannabis is legal are still not allowed to imbibe. CBD can sometimes show up as THC on drug tests, so many drivers tend to avoid using it. However, truck drivers are allowed to get behind the wheel with a blood alcohol level of 0.04%. 

I’ve previously argued that policymakers should consider loosening restrictions around truck drivers’ use of legal marijuana. The federal government and industry at large have doubled down on rooting out truck drivers who use drugs. It’s smart to pull drivers off the road who may be under the influence of cocaine, meth, opioids and other harmful drugs, but the clearinghouse has largely just pushed out those who may or may not be under the influence of marijuana at the time of their testing. 

There’s one major hurdle to nixing marijuana testing while still cracking down on other drugs. Currently there is no capability to test if someone is under the influence of marijuana the same way as for alcohol. Urine tests can reflect marijuana use from weeks ago, while more harmful drugs only appear for hours or days. 

Still, there are smarter ways to reduce truck crashes, as I wrote in 2021:

Tackling our nation’s crumbling infrastructure or bolstering training would be far more effective in saving lives. According to a Department of Transportation study, illegal drugs contributed to 2% of all accidents between an 18-wheeler and passenger car. Meanwhile, brake problems (a factor assigned in 29% of crashes), speeding (23%), unfamiliarity with roadways (22%) and roadway issues (20%) were far more common in such collisions.

‘The industry is rooted… in the previous century’

Cracking down on marijuana use also means the trucking industry is severely limiting who it may recruit, especially among Generation Zs or millennials. Around 22% of Americans under 30 smoke marijuana, according to a 2019 Gallup poll. The American Trucking Associations previously said the high average age of a truck driver is “one of the largest factors” for what they contend is a driver shortage of tens of thousands. Meanwhile, Wells Fargo recently blamed marijuana testing as a leading cause of the driver shortage.

Experts disagree on what’s sparking retention issues in trucking. (Jim Allen/FreightWaves)

A far more pressing reason than trucking retention to soften marijuana laws is the health of our driver population, which totals nearly 2 million. More than 3 million Americans own medical marijuana licenses, according to a 2021 Florida Gulf Coast University study. Around 65% reduced or discontinued their use of another over-the-counter medication, with anxiety, stress and chronic pain cited as the leading ailments they use cannabis to treat. 

Truck drivers can’t use cannabis to treat their own health ailments — even if they are using them off duty. It’s highly concerning considering the slew of health issues that affect drivers, such as rampant cases of musculoskeletal pain and “significant issues affecting their mental health.” 

Meanwhile, truck drivers are far less likely than the average employed American to visit a doctor or have health insurance. Truckers also are at an increased risk for most lifestyle diseases, such as lung cancer and diabetes, than the average American. 

Relaxing marijuana rules won’t solve all of these woes, but it could help. Walter S., a retired truck driver based in Indianapolis who didn’t want his last name used, told me last year in an email that the gap between trucking and the rest of the country was stymying the industry. 

“Guys on prescription meds are still rolling, alcohol is dominant, and the thing that might relax the drivers? Forget it,” Walter wrote. “The industry is rooted in the mindset of the previous century, so alcohol and prescription drugs are accepted.”

I hope you enjoyed this week’s MODES. Please subscribe for newsletters every Thursday. If I missed something, email me at [email protected]

44 Comments

    1. JERRY. SMITH

      I DISAGREE W TESTING FOR MARIJUANA. I GET HOME ON A FRIDAY SMOKE A LITTLE. THEN AGAIN SATURDAY BUT. STOP SO I CAN HEAD OUT SUNDAY 5 AM. DROVE TRUCKS ALL MY LIFE & IM 60 Y.O. HAVE OVER A MILLION MILES .WITH NO ACCIDENTS TICKETS WARNINGS AGAINST. MY CDL BUT BECAUSE I SMOKED I COULD FAIL A DRUG TEST. BUT YET. THEY LET DOCTORS PRESCRIBE PILLS FOR BACK PAIN ETC AND PEOPLE BANG HEROIN & GET IN A TRUCK / PLANE / RUN HEAVY EQUIPMENT OR DRIVE A 4 WHEELER WICH 4 WHEELERS ARE INVOLVED IN 99% OF ACCIDENTS. INCLUDING ROAD RAGE.

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Rachel Premack

Rachel Premack is the editorial director at FreightWaves. She writes the newsletter MODES. Her reporting on the logistics industry has been featured in the New York Times, the Wall Street Journal, Bloomberg, Vox, and additional digital and print media. She's also spoken about her work on ABC News, NBC News, NPR, and other major outlets. If you’d like to get in touch with Rachel, please email her at [email protected] or [email protected]