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Making Roads Safe from Marijuana-Impaired Drivers

April 16, 2019
Trucking research group recommends ways to stem increasing threat to commercial drivers.

A new study urges state and federal governments to take stronger actions to improve the ability of law enforcement to seeks to identify and deter the growing danger of marijuana-impaired driving.

A study of our current state of knowledge about the topic was recently published by the American Transportation Research Institute (ATRI), the nonprofit research arm of American Trucking Associations.

The growing trend of more states choosing to allow both the medical and recreational use of the drug has not been accompanied by advances in methods for effectively addressing marijuana-impaired driving. As a result, this topic is a top-of-mind concern for many truckers, the institute notes. In fact, last year the subject was identified as a top safety research priority by ATRI’s Research Advisory Committee (RAC), made up of industry safety experts.

“While increased access to marijuana has not directly impacted the trucking industry in terms of truck drivers testing positive for marijuana, the increased frequency of marijuana-positive drivers operating on the same roadways as trucks makes marijuana-impaired driving a critical safety issue for the trucking industry,” ATRI’s report points out.

Mike Card, president of Combined Transport Inc., agrees. “It is extremely concerning to motor carriers and our drivers that recreational marijuana is legal in so many states, yet as the ATRI report documents, a valid and widely accepted breathalyzer-type test is not available to law enforcement. ATRI’s study clearly defines a role for federal and state leaders to support law enforcement and others in keeping the roadways safe from those who choose to drive high.”

In particular, the report highlights the importance of training law enforcement in how to identify and collect evidence of marijuana-impaired driving, particularly through the development of more well-trained drug recognition experts (DREs).

“As ATRI’s research identifies, a key tool for combating drugged drivers is deploying additional drug recognition experts,” says Mark Savage, deputy chief of the Colorado State Patrol. “A DRE can bring critical evidence to prosecutors that other tests simply cannot measure.”

Test Methods Inadequate

Although drunk driving can be prosecuted using accurate testing tools, widely-tested and accepted tools and methods are not currently available for marijuana impairment testing, according to the researchers. “As a result, truck drivers in many states now face the significant risk of having legal marijuana users drive impaired (and illegally) alongside their trucks.”

When it comes to alcohol and driving, in recent decades tightened laws and development of accurate testing technology aimed at combatting driving under the influence (DUI) are credited with contributing to an approximately 50% decrease in annual alcohol-related traffic deaths currently versus the 1980s.

Several states that have approved medical or recreational marijuana use also have codified legal protections that prevent employers from taking adverse action against employees for their use of the drug anywhere except when at work. Of course, it is well established that even the most generous of the state marijuana legalization laws do not protect workers in professions where it is banned for safety reasons, such as commercial drivers, train operators and pilots.

Because marijuana is processed by the body differently than alcohol, existing drug testing mechanisms can easily identify past marijuana use by measuring metabolites, but they cannot measure a current state of intoxication.

Although not generally indicative of current state of intoxication, a positive test for past marijuana use can allow for employee termination by many employers, particularly those with strict anti-drug policies or those who employ safety-sensitive transportation workers.

Thus, a simple blood or breathalyzer test—commonly employed by law enforcement when alcohol impairment is suspected—is not ideal for identifying drivers operating under the influence of marijuana. This is due to the body’s mechanisms for processing marijuana’s intoxicant agent, THC.

Of the states that have legalized recreational marijuana, most have set limits on the amount of acceptable THC in blood tests when testing for driver impairment. However, there are several issues related to such tests. Some state laws allow a DUI charge if following an arrest the driver tests positive for THC derivatives in urine, which indicates marijuana use in the previous 30 days but not necessarily recent marijuana use.

Testing Driver Behavior

Identifying, documenting and prosecuting marijuana-impaired drivers depends on each state’s laws, but can be achieved through: observation and documentation of behavior; physical evidence; and drug testing in states where there are THC limits or zero tolerance laws.

Police officers are extensively trained in how to identify impaired driving while observing how a vehicle is being operated, or after an accident on how the driver is behaving. In most cases the officer first conducts a standard field sobriety test (SFST), which involves asking the driver to stand on one leg, walk and turn, and moving an object like a pen or light in front of the driver’s face to see if their eyes jerk.

The Advanced Roadside Impaired Driving Enforcement (ARIDE) program, developed by the National Highway Traffic Safety Administration (NHTSA) and the International Association of Chiefs of Police (IACP), seeks to bridge the gap between SFST and Drug Recognition Expert (DRE) evaluations of impairment. However, only 17 states have more than 20% of officers trained in ARIDE.

DRE’s are specially trained law enforcement officers certified in recognizing and assessing individuals who are under the influence of drugs and alcohol. DREs are a key method that many states, Canada and the European Union use to determine marijuana impairment. DRE impairment determinations are supported by drug tests, which include oral or saliva swabs, urine testing and blood sample testing.

In 2017, there were 8,606 DREs operating in the U.S. who conducted a total of 30,989 enforcement examinations, the researchers found. Marijuana was the most frequently identified substance in these examinations.

The ATRI study also recommends that a number of other steps be taken to deal with the growing problem. These include increased data collection on the frequency and impacts of marijuana-impaired driving; public education and information be widely disseminated concerning the risks of impaired driving; better equipping law enforcement and the court system to intercept and ultimately prosecute impaired drivers; and targeting tax revenue generated from marijuana sales to fund these activities.

“Educating the public on the dangers of marijuana-impaired driving, and of the legal consequences, is critical to preventing drugged driving,” the ATRI researchers stress. “Marijuana users—particularly younger users—do not perceive marijuana as having an impact on driving safety, and in a smaller number of cases, they may believe that marijuana improves driving safety. These beliefs are in direct contrast to the documented effects that marijuana has on driving-critical cognitive functions.”

About the Author

David Sparkman

David Sparkman is founding editor of ACWI Advance (, the newsletter of the American Chain of Warehouses Inc. He also heads David Sparkman Consulting, a Washington D.C. area public relations and communications firm. Prior to these he was director of industry relations for the International Warehouse Logistics Association. Sparkman has also been a freelance writer, specializing in logistics and freight transportation. He has served as vice president of communications for the American Moving and Storage Association, director of communications for the National Private Truck Council, and for two decades with American Trucking Associations on its weekly newspaper, Transport Topics.

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