Smokers, regular or not, keep THC in the blood for days or even weeks after smoking when they have not been under the influence of cannabis ( cannabis dui ) for a long time. While it is legitimate to suspect the intoxication of a driver when he is unable to walk in a straight line, the same tests to determine if he is under the influence of cannabis ( cannabis dui ) do not make a consensus in the scientific community, according to The Marshall Project . "There are few police tools available for alcohol for cannabis," says the news website. While most studies on the subject show that cannabis use is not without effect on the ability to drive a car, the disruption seems comparable to driving with a blood alcohol level below the limit authorized by the Marshall Project-the risk is much greater if the two substances are combined. "The risk of an accident is so minimal that it can be compared to night driving , " according to Rune Elvik, a scientist at the Univers