Washington has seen fatal car crashes involving marijuana more than double since voters legalized the drug there, according to a set of new studies. But that fact may not mean much, the studies found, as legal limits on high driving are arbitrary and unscientific.

Driving and Smoking HighThe reports were released in May by the AAA Foundation for Traffic Safety, a nonprofit research and education group attached to the American Automobile Association.

The first study explored statistics on fatal cannabis-related crashes before and after the drug was legalized in Washington. That happened in November 2012, as did legalization in Colorado.

In terms of percentages, more than twice as many drivers who had recently used cannabis were involved in fatal crashes in Washington, the study found, jumping from 8 percent to 17 percent between 2013 and 2014.

‘Alarming increase’

“The significant increase in fatal crashes involving marijuana is alarming,” Peter Kissinger, president and chief executive of the AAA Foundation, said in a statement. “Washington serves as an eye-opening case study for what other states may experience with road safety after legalizing the drug.”

But the second study casts such dire conclusions into doubt. It found that legal limits and testing methods designed to stop high driving have little scientific support and could land innocent drivers in jail or let real offenders go free. They also make for unreliable data.

Some states apply so-called “per se” limits on the amount of THC a driver may legally have in his or her bloodstream while operating a vehicle. Similar to the 0.08 system used to catch drunk drivers, this approach treats positive test results as presumptive evidence of guilt.

Marijuana impairment tests are unreliable

weed leafResearchers with AAA looked into the lab results of motorists arrested on high driving charges and found the per se approach to be largely ineffective. While it’s well-established that higher blood alcohol concentrations lead to more impairment on the road, the same has not been proven of marijuana. Some drivers with high amounts of THC in their blood may actually be sober.

What’s more, THC metabolites often linger long after their effects have worn off. That means drivers who haven’t been high in hours or even days could end up behind bars.

Because per se methods have little scientific basis, efforts to tally fatal marijuana-related crashes using those standards don’t provide an accurate picture of actual impairment.

In fact, previous studies suggest fatal crashes may be dropping in the wake of legalization. More people who would otherwise drive drunk may be toking and driving instead, or even choosing to smoke pot and stay home. Repeated research demonstrates that driving stoned is significantly less dangerous than driving drunk.


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