Legal Marijuana and Driving: A Public Safety Problem

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Teen girl pulled over in her car by a policeman.

When you’re driving down the highway at 60 miles per hour, you need a clear head. Driving while distracted by your phone or driving under the influence of alcohol both can lead to crashes and tragedy. Driving under the influence of marijuana is also dangerous, because of the way the drug affects the brain and body.

Recent news reports have talked about how drugged driving crashes and deaths have surged since medical marijuana has become legal in more states. Now that marijuana is legal for those over age 21 in Colorado and Washington, the rates of drugged driving are likely to increase even more.

This poses a problem for police and our criminal courts because there isn’t yet a test that can show a person’s marijuana levels the way a “breathalyzer” test can show how much alcohol is in a person’s system in just a few seconds. It also poses a problem for public safety. When people drive after using marijuana, they put themselves, their passengers, and anyone else on the road in danger.

Evidence from driving studies indicates that marijuana can harm a driver’s ability to pay attention, awareness of time and speed, and ability to draw on information gained from past experiences. Impairment increases a lot when marijuana is combined with alcohol.

Another problem is that marijuana stays in your system a lot longer than alcohol, which leaves a few hours after you stop drinking. A recent NIDA-funded study looked at long-term marijuana users very closely. The researchers found that even if a person hasn’t used marijuana in a month, it could still be detected in their blood—which may have an effect on a person’s ability to drive safely.

The bottom line: Use of any mind-altering drug makes it highly unsafe to drive a car and is against the law—just like driving after drinking alcohol.

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