ATRI report reveals issues with marijuana-impaired driving

March 19, 2019

Mark Schremmer


Although marijuana remains illegal for all federally regulated truck drivers, passenger vehicle drivers in several states are allowed to consume THC, the active ingredient in marijuana. According to research conducted by the American Transportation Research Institute, marijuana-impaired driving among four-wheelers can pose a safety risk to the trucking industry.

In a report titled “Marijuana Legalization and Impaired Driving: Solutions for Protecting our Roadways,” ATRI, which is affiliated with the American Trucking Associations, studied the impacts of marijuana-impaired driving and how they can be mitigated. As more states legalize marijuana for recreational use, there has been an increase in passenger vehicle drivers testing positive for marijuana.

“This is concerning to the trucking industry considering the large percentage of truck-involved crashes caused by the actions of car drivers,” the report states. “Further exacerbating this concern is the difficulty faced by law enforcement in deterring marijuana-impaired driving.”

To date, 33 states have legalized marijuana for medical use and 10 states legalized marijuana for recreational use. Laws restricting and punishing marijuana use while driving vary from state to state.

ATRI suggests improvements in data collection, law enforcement training, testing and public outreach can help reduce the risks of marijuana-impaired driving.

Data collection

According to the report, data on marijuana-involved crash rates are not collected at the same rate or with the same level of confidence as those involving alcohol impairment. ATRI cited the National Highway Traffic Safety Administration to highlight this point.

“There is little state level data about the prevalence of use of marijuana by drivers being collected,” NHTSA states. “As states continue to change their laws regarding marijuana use in general and as it relates to driving, this lack of state level data prevents evaluation of the effect of policy changes on driver behavior, including willingness to drive while under the influence of marijuana, as well as the effect of marijuana on crashes, deaths and injuries.”

ATRI suggests the following data points need to be collected at the state and national level:

  • Prevalence of marijuana use while driving.
  • Statistics on the number and type of drug tests given by law enforcement, including rates of positive tests.
  • Number of crashes involving marijuana impairment.
  • Number of marijuana-related driving under the influence citations and convictions, as well as final charges for marijuana DUI citations.

“While a large body of research has not demonstrated a definitive relationship between marijuana intoxication on driving safety outcomes, the need to better understand the role that marijuana intoxication plays in crash causation is becoming a critical issue,” ATRI said.

Law enforcement training

Another issue to be addressed is collecting evidence for possible prosecution. ATRI found that many law enforcement officers lack the appropriate training needed to make a determination that a driver is impaired.

Only 21 states have trained all law enforcement officers in Standard Field Sobriety Test, according to the report. A DUI violation determination involves three steps: vehicle in motion (observing driver or vehicle in motion), personal contact and SFST.

NHTSA and the International Association of Chiefs of Police have developed the Advanced Roadside Impaired Driving Enforcement Program, which seeks to bridge the gap between field sobriety tests and drug recognition expert evaluations. Only 17 have more than 20 percent of officers trained in the program.

Drug recognition experts are specially trained officers who are certified in recognizing and assessing individuals who are under the influence of drugs and alcohol. In 2017, there were only 8,606 drug recognition experts nationwide.

Testing types

Another issue surrounding marijuana-impaired driving is accurately testing for THC levels. Testing done via blood, urine and hair samples does not determine impairment at the time the person was driving since THC levels can stay in the system for several days. Blood samples are also highly invasive, whereas urine samples are vulnerable to tampering. Hair tests can lead to positive results if the person was simply around marijuana smoke.

Colorado, Montana, Nevada, Ohio, Rhode Island and Washington state have laws that limit THC content in a driver’s blood. Most states have not established limits but have established laws making it illegal to operate a vehicle under the influence of marijuana.

For example, in Washington state, a driver is legally intoxicated while driving if, within two hours after driving, he has a THC concentration of 5.00 ng/ml or higher in a blood sample.

Prosecuting marijuana-impaired violations must overcome several hurdles. Arizona requires proof of impaired driving but does not have limits on THC blood concentrations. Massachusetts has challenged the ability of field sobriety tests to accurately identify marijuana impairment.

Public outreach

In its report, ATRI claims that marijuana users do not perceive marijuana as having an impact on driving safety. A small number even believes that marijuana can improve driving safety.

Addressing the issue of misinformation, ATRI suggests several methods to deliver accurate information. Safety campaigns is one such method. NHTSA launched its If You Feel Different, You Drive Different campaign last year.

Publishing statistics also can have a positive effect. Unfortunately, many databases at the state and national level do not differentiate between marijuana and alcohol DUI citations. A more detailed database is needed to highlight any potential dangers with marijuana-impaired driving.


Mark Schremmer, senior editor, joined Land Line in 2015. An award-winning journalist and former assistant news editor at The Topeka Capital-Journal, he brings fresh ideas, solid reporting skills, and more than two decades of journalism experience to our staff.