EMERYVILLE, Calif. – Fatal crashes involving drivers who recently used marijuana doubled after Washington state legalized the drug, according to the latest research by the AAA Foundation for Traffic Safety.

This raises serious concerns about marijuana-impaired driving and enforcement, especially when recent research indicates that legal limits for marijuana and driving are arbitrary and unsupported by science.

Washington legalized marijuana in December 2012. Since then the percentage of drivers involved in fatal crashes who recently used marijuana more than doubled from eight to 17 percent from 2013 to 2014 and one in six drivers involved in fatal crashes in 2104 had recently used marijuana, according to the AAA Foundation for Traffic Safety.

The foundation used the experience in Washington to conduct research into the impact of legalization of marijuana on traffic safety.

To enforce drug-impaired driving laws, many states have created legal limits or per se limits to specify the maximum amount of active THC – the chemical that induces marijuana’s effects – that drivers can have in their systems based on a blood test.

These laws are similar to blood alcohol concentration, or BAC, limits used to enforce driving under the influence of alcohol.

However, researchers examined lab results of drivers arrested for impaired driving and the results suggest that legal limits or per se laws for marijuana and driving are problematic because:

· There is no science showing that drivers reliably become impaired at a specific level of marijuana in the blood. Marijuana levels differ from alcohol where it is clear that crash risk increases significantly at higher BAC levels. With marijuana it depends on the individual. Drivers with relatively high levels of the marijuana in their system might not be impaired, while others with low levels may be unsafe behind the wheel.

· High THC levels may drop below legal thresholds before a test in administered to a suspected impaired driver. It takes an average of two hours to collect blood from a suspected driver because it typically requires a warrant and transport to a facility. Active THC blood levels may decline significantly and could drop below legal limits during that time.

· Marijuana can affect people differently, making it challenging to develop consistent and fair guidelines. For example, frequent users of marijuana can exhibit persistent levels of the drug long after use, while drug levels can decline more rapidly among occasional users.

If a state relies only on standard per se laws regarding blood limits, some unsafe motorists would go free and others would be wrongfully convicted for impaired driving because it is not possible to determine whether a driver is impaired based solely on the amount of the drug in their body.

AAA urges states to use more comprehensive enforcement measure to improve road safety.

Rather than relying on arbitrary legal limits (per se laws), states should use a two-component system that requires (1) a positive test for recent marijuana use, and more importantly, (2) behavioral and physiological evidence of driver impairment.

This system would rely heavily on two current law-enforcement training programs: “Advanced Roadside Impairment Driving Enforcement” (ARIDE) and the 50-state “Drug Evaluation and Classification” (DEC). These programs train law enforcement officers to more effectively recognize drug-impaired driving.

“Marijuana can affect driver safety by impairing vehicle control and judgment. Whether the use of marijuana is legal or not, all motorists should avoid driving while impaired,” said Cynthia Harris , AAA northern California spokesperson. “Drivers who get behind the wheel while impaired put themselves and others on the road at risk.”

Two new studies by the AAA Foundation highlight marijuana and driving:

· Prevalence of Marijuana Involvement in Fatal Crashes: Washington, 2010-2014.

· An Evaluation of Data from Drivers Arrested for Driving Under the Influence in Relation to Per se Limits for Cannabis.

The foundation also is releasing research into marijuana and driving, including:

· Cannabis Use Among Drivers Suspected of Driving Under the Influence or Involved in Collisions: Analysis of Washington State Patrol Data.

· Driving Under the Influence of Alcohol and Marijuana: Beliefs and Behaviors, United States, 2013-2015.

· Advancing Drugged Driving Data at the State Level: Synthesis of Barriers and Expert Panel Recommendations.

· Overview of Major Issues Regarding the Impacts of Alcohol and Marijuana on Driving.

Established by AAA in 1947, the AAA Foundation for Traffic Safety is a 501(c)(3) not-for-profit, publicly supported charitable research and educational organization.

Dedicated to saving lives and reducing injuries on our roads, the foundation’s mission is to prevent crashes and save lives through research and education about traffic safety.

The foundation has funded more than 300 research projects designed to discover the causes of traffic crashes, prevent them and minimize injuries when they do occur.

Visit www.AAAfoundation.org for more information on this and other research.