Survey: users of both alcohol, marijuana take more risks behind the wheel

According to AAA research, drivers who consumed marijuana and alcohol within a 30 day period were more likely to engage in risky behavior like speeding, texting, intentionally running red lights, and aggressive driving.

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CADILLAC — A recent AAA survey found that respondents who reported using both marijuana and alcohol (not necessarily at the same time) tend to take more risks behind the wheel.

According to the research, drivers who consumed marijuana and alcohol within a 30 day period were more likely to engage in risky behavior like speeding, texting, intentionally running red lights, and aggressive driving.

"Regardless of whether marijuana is legal or prescribed, driving under the influence of the drug is illegal and extremely dangerous,‘ said Adrienne Woodland, spokesperson, AAA – The Auto Club Group. “Although some drivers think marijuana makes them a better driver, research shows it can inhibit concentration, slow reaction times, and cloud judgment. That judgement is even more compromised by a marijuana user who also drinks alcohol. It’s important that drivers know the risk that comes with these two drugs and never drive impaired.‘

The AAA Foundation for Traffic Safety's annual Traffic Safety Culture Index found that drivers who use both marijuana and alcohol were significantly more prone to driving under the influence of alcohol versus those who only drink alcohol but do not use marijuana. These motorists identified as someone who consumed alcohol and used marijuana in the past 30 days, and in some cases, they may have used both at the same time. They also engage in various other dangerous driving behaviors far more than drivers who consume either just alcohol or abstain from either drinking alcohol or using marijuana.

Compared to alcohol-only users, drivers who admitted to using both drugs were more likely to report such behaviors as:

• Speeding on residential streets (55%) vs. alcohol-only (35%) vs. marijuana-only (46%)

• Aggressive driving (52%) vs. alcohol-only (28%) vs. marijuana-only (41%)

• Intentional red-light running (48%) vs alcohol-only (32%) vs. marijuana-only (38%)

• Texting while driving (40%) vs. alcohol-only (21%) vs. marijuana-only (24%)

Unsurprisingly, the study found drivers who neither drink alcohol nor use marijuana were considerably less likely to engage in the sorts of risky driving behaviors examined. This Foundation research was published in January 2021 in the peer-reviewed journal Transportation Research Record. 

While other researchers also have found that users of marijuana and alcohol (especially at the same time) take more risks on the road, some findings indicate that the effect of only marijuana may actually lead to less risky driving behavior.

A 2010 study published by the American Journal of Addictions outlines the differences between driving under the influence of marijuana versus alcohol.

The study concluded that while THC does affect a person's motor skills, cognitive and perceptual abilities, it also tends to make them drive more carefully.

"Many investigators have suggested that the reason why marijuana does not result in an increased crash rate in laboratory tests despite demonstrable neurophysiologic impairments is that, unlike drivers under the influence of alcohol, who tend to underestimate their degree of impairment, marijuana users tend to overestimate their impairment, and consequently employ compensatory strategies," the study states.

"This awareness of impairment has behavioral consequences. Several reviews of driving and simulator studies have concluded that marijuana use by drivers is likely to result in decreased speed and fewer attempts to overtake, as well as increased 'following distance.' The opposite is true of alcohol."

When combined with alcohol use, however, the study states that the effects on driving are far more severe.

"Epidemiological studies have been inconclusive regarding whether cannabis use causes an increased risk of accidents; in contrast, unanimity exists that alcohol use increases crash risk," reads the study. "Furthermore, the risk from driving under the influence of both alcohol and cannabis is greater than the risk of driving under the influence of either alone ... Consequently, on the basis of cognitive studies, it seems reasonable to propose that smoking marijuana may increase the risk of having a fatal traffic accident."