• Marijuana is directly linked to impaired driving. A meta–analysis published in the peer-reviewed 2012 edition of Epidemiological Reviews looked at nine studies conducted over the past two decades on marijuana and car-crash risk. It concluded, “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.”i
• A widely cited article in the British Medical Journal from 2012 concluded that marijuana use doubles the risk of car crashes.ii
• Another recent meta–analysis of nine studies found that marijuana “…use by drivers is associated with a significantly increased risk of being involved in motor vehicle crashes.” iii
• For the United States in 2009, 63% of fatally injured drivers were tested for the presence of drugs, which is equivalent to 3,952 fatally, injured drivers. Narcotics and cannabinoids accounted for almost half of all positive results.iv
• Three decades of education on drunk driving and tough laws have had the direct effect of reducing alcohol-related car crashes dramatically in the last thirty years. In fact, a recent survey by the U.S. Department of Transportation found that 1 in 40 nighttime, weekend drivers tested positive for a blood alcohol content (BAC) level of 0.08 — a 70 percent reduction since 1973. The survey tested other drugs for the first time and found that 1 in 12 tested positive for marijuana. Data from peer-reviewed, published research finds that marijuana impairs motor coordination, reaction time, attentiveness, and perception of time and speed.
• In a study of seriously injured drivers admitted to a Levelt 1 shock trauma center, more than a quarter of all drivers tested positive for marijuana. Research conducted at the University of Auckland, New Zealand found that
habitual marijuana users were 9.5 times more likely to be involved in crashes, with 5.6 percent of people who had crashed having taken the drug, compared to 0.5 percent of the control group.
ii M. Asbridge, J. A. Hayden, J. L. Cartwright. Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis. BMJ, 2012; 344 (feb09 2): e536 DOI:10.1136/bmj.e536