Research

Study: 51% of drivers decide whether or not to drive after using cannabis based on how impaired they feel

The Zebra presents a comprehensive survey of drivers in the U.S. who have access to recreational cannabis.

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Intro

With 15 states having now legalized recreational cannabis use (plus Washington, D.C.), more drivers than ever are grappling with decisions about when it is — and isn’t — OK to drive after consuming the drug. 

Laws and best practices for drivers who drink alcohol have been established by decades of science, but research on the effects of cannabis on driving is far more limited. The first states to legalize recreational cannabis were Washington and Colorado almost 10 years ago in 2012. However, there still isn’t clear guidance for drivers and tourists about when it’s safe to get behind the wheel after using cannabis in legal states, leaving drivers largely on their own to decide.

Here’s what we do know:

  • Cannabis causes impairment. Cannabis can impair motor skills, cognitive function and other driving abilities. If you’re impaired or are unsure if you’re impaired, experts agree you shouldn’t drive, but that’s not exactly clear guidance. NHTSA’s recent campaign attempted to turn this idea into a more simple rule for drivers that states, “if you feel different, you drive different.” 
  • Nobody’s really sure how long that impairment lasts. Current recommendations for how long people should wait to drive after consuming cannabis range anywhere from 2 to 24 hours, depending on who you ask. Washington’s Liquor and Cannabis Board recommends at least five hours for inhaled cannabis (or longer if it’s edible). In comparison, Colorado’s state website recommends waiting to drive at least six hours after smoking up to 35 mg of THC and at least eight hours after eating or drinking up to 18 mg.
  • More Americans are in favor of legalization than ever. Cannabis is becoming more accepted nationwide. A Gallup poll from October 2020 shows that 68% of adults support the legalization of marijuana in the U.S. This is the highest support has been for the measure in the past five years. 
  • There isn’t solid evidence that cannabis contributes to car crashes and traffic fatalities. The drug’s role in car crashes isn’t as clear as the link between alcohol and crashes, according to IIHS, which found early evidence that crashes increased in recreational cannabis states. Another study by the National Bureau of Economic Research found that legalization did not affect traffic fatalities in Colorado and Washington. Cannabis’s impact on road safety is still being studied and debated. 
  • Guidelines around cannabis use and driving are unclear. Drivers who drink alcohol can look to established guidelines to know how a beer or two could affect their driving and how long they should wait. Such guidelines haven’t been established for cannabis — and creating them could be complicated. Some states, like Vermont and Massachusetts, have adopted the “if you feel different, you drive different” terminology to provide a guideline for drivers. Other states have per se limits that give drivers a legal limit for THC in the bloodstream. However, because THC can stick around in the body long after consumption, these limits have plenty of critics. In fact, one evaluation from AAA’s Foundation for Traffic Safety states that “a quantitative threshold for per se laws for THC following cannabis use cannot be scientifically supported."

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Experts agree more study is needed, but cannabis’s federal classification as a Schedule I controlled substance adds a tricky barrier. Researchers need federal government approval to use cannabis in studies.

To understand how drivers are currently navigating these difficult choices, The Zebra surveyed 990 drivers who use cannabis in recreational states.

Common cannabis-related terms and definitions 

THC: Short for tetrahydrocannabinol, the psychoactive component of cannabis that makes users feel “high.”

Edible: A cannabis or THC-infused food or drink. The altering effects usually take longer to set in, and they can be longer-lasting and more intense than inhaled cannabis.

Vaping: Using an electronic device that heats cannabis or a cannabis concentrate to release a breathable vapor.

Key Findings

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    51% of drivers decide whether or not to drive after using cannabis based on how they feel.

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    47% of drivers said they noticed at least one driving impairment after using cannabis.

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    74% of drivers chose an alternative to driving high this past year.

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    Only 35% of drivers say they are very likely to know their state’s cannabis and driving laws.

Key finding 1

51% of drivers decide whether or not to drive after using cannabis based on how they feel. 

When it comes to cannabis, there aren’t many rules like there are for alcohol about when it’s okay to drive after consumption. 51% of drivers we surveyed said they decide whether or not to drive after using cannabis based on how they feel.

Is that “feeling'' reliable? 66% of drivers said they feel very or extremely familiar with cannabis and how it affects them. This is the same percentage of respondents (66%) who said they use cannabis at least weekly. This could mean that more frequent cannabis users may feel more in tune with how cannabis affects their bodies, minds and driving abilities.

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When deciding if they’re good to get behind the wheel, 69% of drivers said they can reliably judge if they’re too impaired to drive after using cannabis. But that trust they have in their own abilities does not extend to others. Only 36% of respondents trust cannabis tourists to know if they’re too impaired to drive, and only 43% trusted fellow state residents. When it comes to the cops, 1 in 3 drivers don’t think a police officer can reliably judge when someone is too impaired to drive. 

However, the data we got about ticketing shows that while many of these drivers said they can reliably judge if they’re too impaired, that judgment may be a little, well, cloudy. Of the drivers who were ticketed in the past year, 41% admit they were under the influence of cannabis at the time.

Key finding 2

46.8% of drivers said they noticed at least one driving impairment after using cannabis.

It’s not a secret that cannabis alters brain function. According to the CDC, cannabis can slow reaction time and the ability to make decisions, impair coordination and distort perception (all skills that are pretty crucial for drivers).

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When asked about how long they wait to drive a car after consuming cannabis, 35.5% of drivers say they typically wait 1-4 hours after using cannabis. 33.1% typically wait five or more hours, and 6% of respondents told us they use cannabis while driving. 

But, when asked the shortest amount of time they’ve waited to drive after using cannabis in the past year, 37.2% admitted to driving less than an hour after consumption. Is this long enough? Once again, the jury is out. There aren’t many clear rules around cannabis use and driving. According to guidelines from the state of Alaska, the effects of cannabis can last longer than users think, and the more THC a person smokes or consumes, the greater the impairment will be. When it comes to edibles, Alaska recommends that people wait longer than they think they need to before getting behind the wheel. They state that “the high from marijuana edibles may take up to four hours to peak, and can last for up to 10 hours.”

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When asked about the dangers of driving under the influence of cannabis, 73% of drivers said driving under the influence of alcohol is more dangerous, and 68% said texting and driving is more dangerous. And they might be right. There isn’t a clear answer on how dangerous it is to be under the influence of cannabis while driving.

“I don't think it's a good idea to drive stoned, but it's better than driving drunk.” - 66-year-old woman from Arizona

According to NHTSA, distracted driving claimed 3,142 lives in 2019, and drunk driving was responsible for 10,142. What about cannabis? NHTSA admits that they are still researching to better understand the relationship between cannabis impairment and increased crash risk. However, their Drug and Alcohol Crash Risk Study found that cannabis users are more likely to be involved in crashes, but the increased risk may be because cannabis users are more likely to be young men, who are generally at a higher risk of crashes. Even the CDC states that “it is unclear whether marijuana use actually increases the risk of car crashes.”

Key finding 3

74% of drivers chose an alternative to driving high this past year. 

More than half of drivers (52%) worry about cannabis affecting driving performance. This could be why 74% of drivers do a variety of behaviors to prevent themselves from driving after using. 

38% of drivers got a ride from friends or family instead of getting behind the wheel themselves, and one in three drivers used a food delivery app to prevent themselves from driving under the influence.

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When asked if they plan for a ride before consuming cannabis or alcohol, 56% of drivers plan for a ride before drinking alcohol, but only 37% do before cannabis. The majority of our respondents said they use cannabis to relax/destress or help with sleep, and for 52% of users, cannabis is primarily consumed at the end of the day.

“I don’t ever drive while I’m high, so it’s not a concern of mine. But I don’t want other people to drive while they are high either.” - 39-year-old female from California

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Key finding 4

Only 35% of drivers say they are very likely to know their state’s cannabis and driving laws.

It’s clear that drivers are looking for better guidance surrounding cannabis. Drivers seem to be aware of the limitations of current cannabis driving laws and guidelines, both when it comes to helping them decide when it’s safe to drive and when it comes to law enforcement efforts.

“I never drive when I've used cannabis. There need to be laws about driving after using cannabis, but I don't know how you test for that. It's not safe to drive when high.” - 68-year-old female from California

67% of drivers who drink alcohol say they are very likely to know their state’s alcohol and driving laws (Twice as many as cannabis!)

While only 35% of people said they are very likely to know their state’s cannabis and driving laws, 43% said they follow their state’s laws regarding cannabis use and driving. 

Drivers are seeking stronger and clearer laws surrounding cannabis use. 46% said they support stronger laws against driving under the influence of cannabis, and 60% said the U.S. Federal Government should create national laws and guidelines to address safe driving and cannabis use.

“It's legal here. Honestly, there are enough states with legalization in process or already approved. The feds need to deregulate and pass a federal law.” - 52-year-old man from California

Our survey shows that updated national laws and safe driving guidelines would benefit drivers in legal states, tourists to those states, and drivers in states that will be legal in the future.

Methodology

This report presents the findings of an online quantitative survey of 990 U.S. drivers age 18+ who live in a state where recreational cannabis is legal and who have used cannabis containing active THC in the past year. States include Alaska, Arizona, California, Colorado, Illinois, Maine, Massachusetts, Michigan, Montana, Nevada, New Jersey, Oregon, Vermont, Washington and Washington, D.C. The margin of error for the sample is +/-3% at a 95% level of confidence. The survey was developed by The Zebra and executed by independent research firm Maru/Blue from March 18-29, 2021.

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