Stoned drivers much safer than drunk drivers, and setting legal limits for pot basically useless

Drivers who use marijuana are significantly less likely to crash than drivers who use alcohol, according to a new federal report.

In fact, after adjusting for age, gender, race, and alcohol use, stoned drivers are no more likely to crash than drivers who had not used any intoxicating substances, reported the Washington Post.

The National Highway Traffic Safety Administration study found no statistically significant change in the risk of a crash associated with marijuana use, although drivers with a blood-alcohol content of 0.05 or above were at least seven times more likely to be involved in a wreck.

“At the current time, specific (marijuana) concentration levels cannot be reliably equated with a specific degree of driver impairment,” the NHTSA study found.

The researchers pointed out that drugs are absorbed by the body in different ways, so it’s difficult to measure a specific level of impairment in the same way that blood-alcohol levels can be detected.

"Most psychoactive drugs are chemically complex molecules, whose absorption, action, and elimination from the body are difficult to predict," the researchers said. "Considerable differences exist between individuals with regard to the rates with which these processes occur. Alcohol, in comparison, is more predictable."

THC, the psychoactive component in marijuana, can be detected in heavy users of the drug for days or even weeks after use, and long after it would cause impairment.

Several states -- including Colorado, where recreational pot use is legal – have passed laws to define driving-related impairment levels for marijuana.

But the blood THC threshold of 0.5 nanograms per milliliter, which is the level set by Colorado, is essentially meaningless in relation to driving impairment.