• Marijuana affects psychomotor skills and cognitive functions critical to driving including vigilance, drowsiness, time and distance perception, reaction time, divided attention, lane tracking, coordination, and balance.  Capler et al., 2017; Compton, 2017; Strand et al., 2016.   GHSA Jennifer’s Messengers.
  • Both alcohol and marijuana’s THC can impair driving skills.  The level of impairment depends, among other factors, on the amount of drug consumed by the driver.  The average THC-impaired driver is less impaired and less dangerous than the average drunk driver, but only a few drivers are average.  Drivers consuming high doses of either drug are the most dangerous to innocent victims.  Someone on a high dose of marijuana will be more impaired than someone on a low dose of alcohol.
  • Multiple studies support the estimate that drivers double their vehicle crash after using marijuana, Hartman RL, Huestis MA. Cannabis effects on driving skills.  IASIC.  Those estimates are based on results of some highly impaired drivers as well as many who have either low levels of impairment or those who may test positive for THC but are not noticeably impaired.  Crash risk may be increased by a factor of as much as 10 for drivers who are so impaired that they are convicted of driving under the influence due to THC only.  Colorado convicts nearly 900 drivers annually of driving under the influence of THC only.  Driving Under the Influence of Drugs and Alcohol.  Colorado Department of Criminal Justice, Jan. 2022.
  • Cannabis is the most prevalent illicit drug identified in impaired drivers.  IASIC
  • Legalizing marijuana for recreational use does increase overall crash rates.  IIHS-HLDI President David Harkey.
  • Marijuana was the most frequent drug found in drivers involved in fatal crashes in Massachusetts from 2013-2017, 31%.  The Baker Administration, Boston Globe.
  • Crash rates spiked with the legalization of recreational marijuana use and retail sales in California, Colorado, Nevada, Oregon and Washington.  Injury and fatal crash rates in California, Colorado, Nevada, Oregon and Washington jumped in the months following the relaxation of marijuana laws (with retail sales) in each state.  The Insurance Institute for Highway Safety and the Highway Loss Data Institute study.