Pot Smoking Doubles Risk of Car Accident Study is first to probe link between marijuana and collisions: researchers By Matt Cantor, Newser User Posted Feb 10, 2012 12:40 PM CST 107 comments Comments Marijuana use can double the risk of a car accident, a study says. (Shutterstock) (Newser) – Smoking marijuana three hours or less before getting behind the wheel nearly doubles your chance of a major car crash, a study suggests. It's the first study to look at the link between cannabis and crash risk, the Canadian researchers believe. They examined study data for more than 49,000 collision victims, limiting their research to crashes that didn't involve alcohol, CBC reports. "The level of impairment might not be as severe as alcohol intoxication, but it's there and it does require a public health response," says an expert.