While a considerable body of science has established that marijuana does impair driving, many remain convinced that pot does not impair driving. Many believe it improves driving. What are the facts as we know them now?

There is a commonly held belief that pot results in slower driving. That finds scientific support. The obvious, and incorrect conclusion drawn is that slower driving and reduced tailgating results in safer driving. No one argues that a greater following distance is a safer driving practice. It appears to be the result of a coping behavior to compensate for the documented slower reaction time. Additionally, slower driving is not necessarily safer, and in fact may be more dangerous.

While a greater following distance is safer, a surprise combined with a slower reaction time is not overcome by slower driving or by greater following distances.

Experimentation shows that marijuana results in less effective peripheral vision, sometimes to the point of “tunnel vision.” While the more experienced user might be able to compensate by intentionally scanning the field of vision, the effect does not go away. Peak impairment occurs generally from ½ hour to three hours after imbibing smoke or vapor. (Edible impairment last much longer.)

One of the key challenges in studying marijuana driving impairment is the subtly of the impact on driving. Unlike the dramatic impairing effects of alcohol on driving, pot’s impairment is more subtle. While some drunk drivers believe that they are driving wonderfully, pot produces the opposite impact. In some studies, after smoking, subjects would say things like “Are you crazy? I’m not driving. I’m too stoned!”

Compounding the scenario, pot and alcohol work synergistically. The whole is greater than the sum of the parts.

Key to this issue is education. The myth that pot results in better driving, and the lack of knowledge of the power of the combined effect of pot and alcohol must both be addressed by accurate, non-political education. The facts cannot be swept under the rug or underestimated. It is noteworthy that the increase in accident risk from marijuana alone is in fact a fraction of the increase in risk from alcohol-fueled driving. It does not improve driving.