Setting legal limits for pot & driving 'meaningless,' AAA study says

Fatal crashes involving drivers who use marijuana have doubled in Washington after The Evergreen State legalized the drug in 2012, according to the latest impaired driving research by the AAA Foundation for Traffic Safety.

In the study, researchers found the number of  drivers involved in fatal crashes, who had a detectable level of active THC – pot’s main chemical component — in their blood, increased from 8 to 17 fatalities between 2013 and 2014. In addition, one in six drivers involved in fatal crashes in 2014 had recently used marijuana.

The AAA findings raise serious concerns about drug-impaired driving in at least 20 states that have legalized pot or are considering legalization this year, said Peter Kissinger, the Foundation’s president and CEO.

The study offers several conclusions:

  • First, there is no reliable, scientific way to show that drivers become impaired at a specific level of marijuana in the blood because pot can affect people differently, making it more challenging to develop consistent, fair legal guidelines. It’s simply not possible today to determine whether a driver is impaired based solely on the amount of marijuana in their body;

  • Second, setting such threshold limits are meaningless and arbitrary because unlike alcohol where there’s a clear-cut crash risk that increases at higher blood alcohol content (BAC) levels, marijuana use is different. Based on the research, high levels of THC — the main chemical component in pot — may drop below legal thresholds before a test is administered to a suspected impaired driver.

Since more people are using marijuana — legally and illegally — and many states are considering legalization for medical or recreational purposes, lawmakers are under tremendous pressure to pass threshold limits, known as per se limits, on driving and marijuana along the same lines as driving and alcohol.

Seventeen states already have implemented various per se limit laws for marijuana. Four states — Alaska, Colorado, Oregon and Washington — and Washington DC have legalized the recreational use of pot. Connecticut is one of 20 states that have legalized marijuana for therapeutic and medicinal purposes.

Recognizing that drugged driving is a growing problem nationally, AAA urges state lawmakers to focus on impairment, rather than on flawed, arbitrary threshold levels. This means developing more comprehensive law enforcement measures to improve road safety.

Rather than relying on arbitrary legal limits, states should use a two part systems that includes:

A positive test for recent marijuana use, coupled with behavioral and physiological evidence of driver impairment.

To do this, law enforcement would rely heavily on two current law enforcement training programs: ARIDE (Advanced Roadside Impaired Driving Enforcement); and the DEC (Drug Evaluation and Classification), both which train officers to recognize drug-impaired driving.

For an in-depth explanation of the studies and related research on marijuana and driving, visit

The AAA Foundation for Traffic Safety is a not for profit, publicly supported charitable research and educational organization dedicated to saving lives and reducing injuries on our roads. Its mission is to prevent crashes and save lives through research and education about traffic safety.