Last Updated: 10/9/2023

With more and more states legalizing marijuana for both recreational and medical use (Currently, 38 states and the District of Columbia have legalized it for the latter; four, plus the District of Columbia, have legalized it for the former), it’s important to understand the effect that marijuana has on driving.

This information will be of particular use to those who may be trying to prove negligence in an accident with an intoxicated driver. To understand that effect, researchers at the University of Iowa performed an in-depth study on the effects of marijuana on driving.

The Study: 18 Men & Women Drive Impaired

Researchers chose 18 men and women, of ages ranging from 21 and 37, to participate in the study. Participants were given ten minutes to drink either mixed drink or a glass of plain juice with an alcohol rimmed glass, the juice topped with alcohol to mimic the taste of a mixed drink. The mimicked mixed drink was aimed at getting participants’ blood alcohol levels to .065 percent, still below the legal limit. Then, they were given 10 minutes to inhale either a placebo or vaporized cannabis.

Next, participants entered a vehicle mounted on a dome—the simulator—and were asked to ‘drive.’ They were assessed on three things, named below.

  • Weaving within the lane
  • How often the car left the lane
  • Speed of weaving

The Results

The results of the study were this: drivers who had inhaled the marijuana showed similar weaving patterns to those of drivers with a BAC of .08 percent. However, those who had only vaporized cannabis—and not alcohol—only demonstrated weaving within the lane; drivers who had alcohol in their systems failed in all three categories.

Impairment can be demonstrated using Breathalyzer tests or/and blood reports collected at the time of the accident. Sometimes, the testimony of others—such as a bartender who served a drink to the driver before the accident—can also be used as evidence.

Filing a Claim for a Car Accident Caused by Impaired Driving

If you’ve been in a car crash caused by impaired driving and have suffered injuries as a result, take action today by filing a claim or consulting with an attorney about the possibility of filing a personal injury lawsuit.

The latter must be filed within two years’ time, or the right to recover damages is lost. For help understanding how to prove impairment, negligence, and liability, call Walker, Billingsley & Bair today at (888) 435-9886 now. 

Corey Walker
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With over 28 years legal experience, Corey has been recognized for his work as an injury attorney.
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