Study finds connection between legal marijuana and fatal car crashes

A new AAA study of the impact of Washington’s legalization of marijuana found traffic fatalities doubled over the course of two years.
A new AAA study of the impact of Washington’s legalization of marijuana found traffic fatalities doubled over the course of two years. –Teresa Crawford / AP

A new study by a top automotive safety organization suggests a connection between legalized marijuana and fatal traffic crashes.

The survey by the AAA Foundation for Traffic Safety found fatal crashes involving marijuana more than doubled in Washington after marijuana was legalized for recreational use in late 2012.

AAA found the effect on driving habits was delayed about nine months from the passage of the legislation in December 2012, so the organization compared statistic from 2013 to those from 2014.

AAA found 49 drivers involved in fatal crashes had marijuana in their system in 2013. That number jumped to 106 drivers in 2014, an increase from 8 to 17 percent of all fatal crashes. Some of these drivers also had alcohol or other drugs in their system at the time of the crash.


For comparison, 31 percent of all traffic deaths nationwide in 2014 involved a driver under the influence of alcohol, according to the Centers for Disease Control and Prevention.

Implications for Massachusetts

In November, Massachusetts voters are scheduled to decide on a ballot measure that will authorize marijuana for recreational use. A recent poll found voters are split on the issue.

Peter Kissinger, President and CEO of the AAA Foundation for Traffic Safety, said the study on the impact of Washington’s marijuana legalization and road safety is “eye-opening’’ for what other states may experience.

“The significant increase in fatal crashes involving marijuana is alarming,’’ said Kissinger in a statement.

Mary Maguire, public affairs and legislative director for AAA Northeast, said the study “sends up a red flag’’ for states considering whether to legalize recreational marijuana.

“The major takeaway of this study is we want to create awareness among drivers that marijuana can impair safety,’’ said Maguire in a phone call with


The report notes that some states have implemented legal limits known as “per se limits’’ in an effort to fight drug-impaired drivers. The concept of per se limits is similar to the concept of the .08 blood alcohol content limit imposed for driving under the influence of alcohol.


Per se limits outline how much tetrahydrocannabinol, the key chemical component of marijuana, drivers can have in their system. But accurately measuring how much THC a driver has in their blood is more complicated than measuring a motorist’s BAC.

AAA notes that marijuana can have different impacts on different individuals. And because blood tests are used to measure an individual’s THC levels, the driver’s THC levels could drop below legal limits during the time it takes to legally obtain a suspect’s blood and conduct an analysis.

Instead of strict legal limits, AAA instead recommends states implement a two-component system to monitor motorists under the influence of marijuana. First, a test would determine recent marijuana use, but second, and more importantly, states would rely on behavioral evidence of driver impairment.

To meet the second requirement, Maguire says, police and other law enforcement personnel would need to be trained in programs like Advanced Roadside Impairment Driving Enforcement or Drug Evaluation and Classification to detect drug-impaired driving behavior.

“Driving is already a demanding task and when you add a drug that impairs our ability to perform that task effectively, it’s concerning,’’ said Maguire.

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