Cannabis does not impair driving ability

According to the U.S. National Institutes of Health (NIH) free digital archive of biomedical and life sciences journal literature, research shows that stoned drivers have a lower accident rate than completely sober drivers. Several on-road driving studies funded by the U.S.Department of Transportation proved that "The THC-only drivers had an [accident] responsibility rate below that of the drug-free drivers, as was found previously by Williams and colleagues (1986)" and "There was no indication that cannabis by itself was a cause of fatal crashes." (see: Incidence and Role of Drugs in Fatally Injured Drivers K W Terhune, 1992 p. 100, Drugs in fatally injured young male drivers. A F Williams, 1985 -- Drugs in Fatally Injured Young Male Drivers

Drivers in whom alcohol alone was present were more likely to be responsible for their crashes than were drug-free drivers (92 percent versus 71 percent, x2 = 15.75, P < x2 =" 1.47,">0.20).

Fifty-three percent of the 19 drivers in whom marijuana alone was found were estimated to be responsible for their crashes, compared with 71 percent of the 78 drug-free drivers (X2 = 1.47, P > 0.20).

Here are some other articles on the subject:

The Truth About Driving When You're High on Marijuana

Marijuana and Driving: A Review of the Latest Scientific Evidence

Developing Science-Based Per Se Limits for Driving under the Influence of Cannabis (DUIC)