In 2012, the Colorado Department of Transportation (“Colorado DOT”) reported that 12.2 percent of those drivers who were tested for illicit drug use after fatal traffic accidents, tested positive for “marijuana only.”

Overall, even without testing, at least 7.4 percent of all traffic fatalities are known to involve drivers who had detectible levels of THC in their blood following the accident.

The Colorado DOT’s Drugged Driving Statistics for 2006-2011 showed a 16-percent decrease in the overall number of traffic fatalities in the state. Conversely, the same six-year period showed a 112-percent increase in the number of fatalities that involved drivers testing positive for “marijuana only.”

Of course, many more drivers tested positive for poly-drug abuse, including marijuana and other illicit drug use.

The study also showed that in 2006, 28 percent of drug-related crash fatalities involved drivers testing positive for marijuana. That number increased to 56 percent in 2011, and remained high at 45.5 percent in 2012.

Notably, a 2011 meta-analysis looked at nine studies conducted over the past two decades on marijuana and car-crash risk, and concluded that drivers who test positive for marijuana or self-report using marijuana are more than twice as likely as other drivers to be involved in motor vehicle crashes.

Similarly, a 2010 study showed that 28 percent of fatally injured drivers and more than 11 percent of the general driver population tested positive for non-alcoholic drugs, with marijuana being the most commonly detected substance.

The available statistics obviously reflect the impact of marijuana use on the number of over-the-road fatalities prior to the legalization of “recreational” marijuana in Colorado.

Unfortunately, it can only follow that the recent legalization of “recreational” marijuana, and the opening of dispensaries on January 1, 2014, will only increase marijuana use and increase the number of drivers who can and will drive under the influence of marijuana.


Crippa, J.A.S., et al., “Pharmacological interventions in the treatment of the acute effects of cannabis: a systematic review of literature,” Harm Reduction Journal, 9:7 (2012).

Mu-Chen Li, Joanne E. Brady, Charles J. DiMaggio, Arielle R. Lusardi, Keane Y. Tzong, and Guohua Li, “Marijuana Use and Motor Vehicle Crashes.” Epidemiologic Reviews (2010), at 3, 6.