One controversial aspect of the marijuana legalization debate centers on the impact marijuana has on driving a car. The states that have legalized personal use have drawn a hard line on driving and marijuana, criminalizing trace amounts of THC in the bloodstream. Other states like Oklahoma and Arizona have zero tolerance laws. These limits seem arbitrary because the effects of marijuana on driving are not well understood. The impact that alcohol has on a person’s ability to operate a vehicle is well documented and understood, yet in comparison there is little hard data examining marijuana and driving. In light of what some states are doing, Congress has been interested in answering this question too. NHTSA has conducted a landmark study to more fully understand what connection marijuana has with motor vehicle accidents. The results that were released in early 2015 are surprising.

NHTSA Study Finds No Correlation between Driving While High and Car Crashes

This first large scale study to try and better understand this issue. Researchers wanted to discover the actual real world consequences of driving while high. The study took place in Virginia Beach, Virginia, and looked at over 3,000 drivers. While stoned drivers increased the risk of crash by 25%, when researchers adjusted this figure for variables such as age, gender, ethnicity, the number shrank and became statistically insignificant. At the same time, researchers determined that drivers with a .08 BAC of alcohol doubled their risk of accident. Drivers with a .10 BAC or higher were 6 times as likely to crash, and drivers with a .15 BAC were 12 times as likely.

The effects of marijuana have been harder to objectively pin down and measure. The impact that smoking or ingesting marijuana has on the human body and its motor skills and cognitive functions has proved elusive. Alcohol is gradually absorbed and eliminated in the body. It can be measured linearly, and impairs people more or less the same way. The impacts of marijuana, on the other hand, can vary sharply from person to person.

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