Don't drink and drive. Don't smoke and drive. Don't text, or eat, while driving. And don't drive tired. All of them increase your risk of crashing, so don't do them. But that said: the increases are different depending on the substance.
According to a new study from Guohua Li, a professor of epidemiology and anesthesiology and the founding director of the Center for Injury Epidemiology and Prevention at Columbia University, driving on alcohol is at least seven times more dangerous than driving on pot.
In the study titled “Drug use and fatal motor vehicle crashes: A case-control study” Li calculated that the "odds ratio" of a fatal crash while driving on pot is 1.83, or almost double that of driving sober, where the odds are 1. That's bad, right?
Now look at the estimated odds of a fatal crash while driving on booze: 13.64.
That means boozed driving is, statistically, 7.45 times more dangerous than stoned driving.
Li's nationwide study looked at 737 drivers killed in collisions in 2007 and used the 2007 National Roadside Survey of Alcohol and Drug Use by Drivers to determine the risk of a fatal accident by drug. Booze proved by far the most dangerous, second only to booze combined with other drugs (odds ratio 23.24) like depressants, stimulants, cannabis, "narcotics", and multiple drugs.
Driving on legal depressants alone - like Vicodin - yields an odds ratio of 4.83, which is about 2.6 times more dangerous than pot. Adderall and other stimulants increase risk of fatal collision by 3.57, or about double the risk of driving on pot.
So basically, driving on pot - while not as safe as driving sober - it is quantitatively less dangerous than driving on legal alcohol, legal Vicodin, or legal speed.
Now put down your phone and drive.