On Nov. 8 voters in California, Maine, Massachusetts and Nevada approved ballot measures to legalize recreational cannabis. It is now legal in a total of eight states. And this creates potential problems for road safety. How do we determine who’s impaired and who’s not?
The effects of alcohol vary based on a person’s size and weight, metabolism rate, related food intake and the type and amount of beverage consumed. Even so, alcohol consumption produces fairly straightforward results: The more you drink, the worse you drive. Factors like body size and drinking experience can shift the correlation slightly, but the relationship is still pretty linear, enough to be able to confidently develop a blood alcohol content scale for legally determining drunk driving. Not so with marijuana.