For years individuals and organizations everywhere have talked about, and continue to work on combating, the dangers of alcohol-impaired driving. As a result, there has been a significant reduction in alcohol-impaired fatalities. However, impaired driving due to drugs other than alcohol, sometimes called “Drugged Driving,” is a growing concern across the United States and beyond. One of the most common drugs found in substance-impaired driving fatalities is marijuana.
Mr. Chris Halsor is the Traffic Safety Resource Prosecutor (TSRP)  in Colorado, where marijuana was first approved by state residents for medicinal use, and more recently for legal recreational use.  With the changes in the law,  Mr. Halsor has seen a troubling increase in drugged driving cases involving marijuana.
Impairment from Marijuana
Based on the science and the research, there is no question that marijuana impairs a person’s mental and physical? abilities. It is wrong to believe that marijuana use does not result in impaired driving. It is a scientific fact: Marijuana use increases the risk of being in a fatal crash.
Of significant concern is the public’s misunderstanding of the signs of marijuana impairment. Message after message has shown alcohol-impaired individuals with slurred speech, poor balance, and problems walking. Mental impairment is actually a greater issue because 1) driving is a complicated task requiring a person to focus on a number of critical factors simultaneously, and 2) alcohol affects a person’s mind and judgment before the physical signs are visible—meaning a person is already mentally impaired by the time the physical signs are observed. Mr. Halsor noted that the predominant marijuana-induced impairment affects a person’s judgment. The impairment is less about the physical response, but that does not make it any less dangerous than alcohol.
The increasing potency of Delta 9 THC is another concern when considering a person’s impairment. Delta 9 THC is the active impairing ingredient in marijuana. Several years ago the THC concentration was typically under 10%, even as low as 2-6% in a “joint.” Now, the potency is significantly higher and marijuana stores in Colorado advertise this increased potency. It is not uncommon to see ads for 20% potency or greater. It has become a race to the top, resulting in greater impairment.
Putting the THC concentrate into a variety of foods also creates problems. Adding the concentrate to food products results in delayed impairment. People consume these products, do not initially feel any effects and then drive, with the effects impacting them while driving.
Drugged Driving and Per Se Drug Laws
Many states have passed a ‘per se’ law, similar to the .08 breath alcohol concentration (BrAC) per se law for alcohol. Colorado passed a modified per se law that allows jurors to infer impairment if a person has 5 nanograms or greater of THC in their blood.
One argument against a per se law is that marijuana stays in the body for up to 30 days. However, Delta 9 THC is generally in the blood only 1 to 3 hours. The THC that is found in the body days later is THC-COOH, an inactive non-impairing metabolite.
Shortly after NTSB’s announcement of the NTSB Most Wanted List in January 2014, the Traffic Safety Guy was able to briefly speak with NTSB Board Member Dr. Mark Rosekind. I asked him about substance impaired driving and the issues marijuana is causing for safe driving. His response is part of this episode.
- NIDA – Marijuana Abuse
- NTSB – Most Wanted List
- ONDCP – Drugged Driving
- The Pew Charitable Trusts – How High is Too High to Drive?
- Fatal Car Crashes Involving Pot Use Have Tripled in U.S.
- Trends in Alcohol and Other Drugs Detected in Fatally Injured Drivers
- NHTSA – 2007 National Roadside Survey of Alcohol and Drug Use by Drivers
- NDAA – Between the Lines – A New High in Colorado
- Traffic Safety Guy Video – NTSB – Most Wanted List
- Highway to Safety Podcast Episode – Drugged Driving
 A TSRP provides traffic-related education, research and technical assistance to prosecutors and law enforcement, with an emphasis on impaired driving.
 Marijuana is still considered an illegal drug by the U.S. Federal Government; thus, there is a dispute on whether or not the drug is legal.
 This episode is not a discussion on the pros and cons of legalizing marijuana. The focus is marijuana’s impact on traffic safety.