You should watch those assumptions.   --   Marijuana is not alcohol. The preponderance of the research shows marijuana consumption is NOT a significant cause of auto accidents. In 2015, the Drug and Alcohol Crash Risk report, produced by the U.S. Department of Transportation's National Highway Traffic Safety Administration, found that while drunken driving dramatically increased the risk of getting into an accident, there was no evidence that using marijuana heightened that risk. 

In fact, after adjusting for age, gender, race and alcohol use, the report found that drivers who had recently consumed marijuana were no more likely to crash than drivers who were not intoxicated at all.