State Marijuana Impaired Driving LawsPosted by On

Driving under the influence of illegal drugs is causing an increasing number of accidents and fatalities.

Close to 18 percent of all fatally injured drivers tested positive for some sort of illegal drug in 2009, according to National Highway Traffic Safety Administration. In a 2014 survey, approximately 20 percent of weekend and or nighttime drivers tested positive for illegal, prescription or over-the-counter medications.

With the passage adult use laws in four states, and medical marijuana laws in many others, there is increased interest in marijuana-impaired driving. Check out this 50-state map that shows marijuana impaired driving and state marijuana laws.


Adults over 21 can grow, purchase, possess and consume specified amounts of marijuana, is termed as legalized.

  • Legalized for medicinal use only means that adults with a medical license can grow, purchase, possess and consume specified amounts of marijuana.

  • Legalized means that the state has made possession of marijuana a civil-rather than criminal-offense.

  • Driving Under Influence of Drugs makes it an offense for a driver to have marijuana in their body while operating a motor vehicle.

  • Under Influence of Drugs standard requires the driver to be under the influence of or affected by marijuana.

  • Incapacity Driving Under Influence of Drugs standard requires the marijuana in a driver’s system make the driver incapable of driving safely. The prosecutor must show a connection between drug ingestion and the incapacity of the driver.

* There are 13 states that have approved medical use of low-THC cannabis/marijuana products, not shown on the map.

In Colorado, Illinois, Montana and Washington, anyone who drives a motor vehicle and has a THC blood concentration of 5 nanograms or more, is presumed to be guilty of driving under the influence. Nevada and Ohio statutes establish a threshold of 2 nanograms of illegal substances per milliliter of blood. Pennsylvania’s administrative law establishes the threshold at 5 nanograms. Other states have perse laws but have not established threshold for marijuana.

  • According to NHTSA, there is evidence that marijuana use impairs psycho-motor and lane tracking skills, and cognitive functions. Marijuana’s role in contributing to the occurrence of crashes is still unclear.

  • Blood tests for drugs other than alcohol are inconsistently performed by law enforcement in many states, and many drivers who are involved in crashes are found to have both drugs and alcohol in their system.

Sources: National Highway Traffic Safety Administration, National Conference of State Legislatures, 2015.


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