Research

Study: 60% of Drivers Who Use Marijuana in Legal States Drive Under the Influence

BASED ON A SURVEY OF 811 DRIVERS WHO USE MARIJUANA IN 10 RECREATIONAL STATES AND WASHINGTON, D.C.

The Zebra presents the most comprehensive survey yet among drivers in the U.S. who have access to recreational marijuana.

Intro

More drivers than ever are grappling with decisions about when it is — and isn’t — OK to drive after consuming marijuana, which is now legal for adults to use recreationally in 10 states and Washington, D.C.

Laws and best practices for drivers who drink alcohol have been established by decades of science, but research on the effects of marijuana on driving is far more limited.

Here’s what we know:

  • Marijuana causes impairment. Studies show that marijuana can impair motor skills, cognitive function, and other driving abilities. If you're impaired or are unsure if you're impaired, experts agree you should not drive.
  • It’s unclear how long impairment lasts. Research is underway to establish how long drivers should wait to drive after consuming marijuana, but current recommendations range anywhere from 2 to 24 hours, depending on who you ask. Washington’s Liquor and Cannabis Board recommends at least 5 hours for inhaled marijuana (or longer if it's an edible). Blood tests can show if someone has used marijuana, but not how impaired a driver is. Regular users can test positive for THC for days after their last use, even though impairment likely lasts just hours.
  • Marijuana's contribution to car crashes and traffic fatalities is unclear. Marijuana’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 marijuana states. Marijuana’s impact on road safety is still being studied and debated.
  • Guidelines around marijuana use and driving are limited. 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 marijuana — and creating them could be complicated. Colorado suggests that occasional users are likely to be impaired after using 10mg of THC or more, but individual results vary.

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

In the meantime, it’s difficult for public safety officials to issue guidance about when it’s safe to get behind the wheel again after using marijuana in legal states, leaving drivers largely on their own to decide.

In order to understand how drivers are currently navigating these difficult choices, The Zebra launched the most comprehensive survey yet among drivers who use marijuana in recreational states.

Definitions

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

Edible: A marijuana 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 marijuana.

Vaping: Using an electronic device that heats marijuana or a marijuana concentrate to release a breathathable vapor.

Key Findings

Almost 60% of drivers who use marijuana in legal states admit to driving under the influence

Most drivers decide if they’re OK to drive under the influence of marijuana based on how impaired they feel

Nearly half of drivers noticed that their driving skills were impaired while they were under the influence of marijuana

Drivers are seeking better guidelines around marijuana use and driving, but they’re skeptical of regulations


Key Finding 1

Almost 60% of Drivers Who Use Marijuana in Legal States Admit to Driving Under the Influence

Drivers are making drastically different choices when it comes to driving and marijuana consumption. Some say they never drive after using marijuana, while others thought it was perfectly fine to use marijuana while behind the wheel

While almost 60% of drivers (59.1% of them combined) admitted to driving under the influence of marijuana, "influence" can mean different things to different drivers.

How impaired a driver is — and for how long — depends on many factors, including the driver’s personal level of tolerance, how they use marijuana (by consuming edibles or inhaling it), and how much they use at a time.

A closer look at drivers’ marjuana habits shows:

68% of drivers said they usually wait at least 2-4 hours before attempting to drive after using marijuana, but 26% said they typically waited less than an hour. The remaining 6% don't think about or know their own habits. 

When drivers were asked about the shortest amount of time they’ve waited to drive after using marijuana in the past year, 41.5% had waited less than an hour.

Survey respondents' other marijuana habits include: 

Method

59% of drivers said they primarily inhale marijuana through smoking or vaping, while 18% primarily eat it by way of marijuana edibles. Another 20% said they used both methods of consumption.

Frequency

50.3% said they consumed marijuana at least 2-5 times per week.

Quantity

The amount of marijuana that respondents said they consumed varied significantly, but the most popular dosage was ⅓-½ gram (about the size of one joint).

These findings indicate that drivers have a wide spectrum of marijuana habits that could impact their driving abilities in significantly different ways. 

So how do drivers decide when and whether they’re sober enough to drive safely?

"It doesn't matter how much I smoke, I drive fine."


Key Finding 2

Most Drivers Decide if They’re OK to Drive Under the Influence of Marijuana Based on How Impaired They Feel

Of the drivers who admit to driving under the influence of marijuana, most put at least some consideration into their level of impairment before taking the wheel.

The most popular consideration drivers relied on was how impaired they feel.

While 60% of drivers appeared willing to trust their own feelings, they notably did not endorse it as a reliable consideration for all drivers who use marijuana.

This may be notable, as almost half of the drivers who admitted to driving under the influence of marijuana reported experiencing at least one impairment while behind the wheel.

"I have a harder time following directions. I have to turn up the volume on my GPS so it reminds me when to turn so I don't miss it."


Key Finding 3

47% of Drivers Felt Impaired While Driving Under the Influence of Marijuana

While just over half of drivers (53%) who said they drive under the influence of marijuana didn’t recall any negative impacts on their driving abilities, the rest (47%) noticed driving impairments.

About 5% of drivers said they received a traffic ticket while under the influence of marijuana, though only 2.2% of surveyed drivers were cited in the past year for a DUI violation (for drugs and/or alcohol).

Though many drivers noticed impairments while driving under the influence of marijuana, most respondents still see it as safer than other dangerous driving behaviors.

54% said texting and driving was more dangerous than driving under the influence of marijuana.

60% said drinking alcohol and driving was more dangerous than driving under the influence of marijuana.

40% said were "very likely" to plan for a ride before drinking alcohol, but only 25% said the same for marijuana.

"It would be nice if there was some sort of device (sort of like a breathalizer for booze) that could measure your THC level."


Drivers Are Seeking Better Guidelines, But They’re Skeptical of Current Regulations

Drivers seem to be aware of the limitations of current marijuana 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.

Only 1 in 3 drivers think their state’s marijuana driving laws are effective.

Only 1 in 3 drivers think police can accurately assess marijuana impairment.

Drivers highlighted a variety of opinions and concerns about driving behavior for marijuana users — and how that behavior should be regulated.

The Zebra’s report presents the findings of an anonymous online survey of 811 legal marijuana users conducted in March 2019. For more information, download the full report.

For more findings and analysis, download the full report.

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