Cannabis Use and Motor Vehicle Accident Risk
"We found only limited evidence to support the claim that cannabis use increases accident risk. Participants who had driven under the influence of cannabis in the previous year appeared to be no more likely than drug-free drivers to report that they had had an accident in the previous 12 months. Prima facie, this would seem to suggest that cannabis-intoxicated driving is not a risk factor for non-fatal accidents. In this sense, the results would support those of Longo et al. (2000b) who found no relationship between recent cannabis use and driver culpability for non-fatal accidents."
Jones, Craig; Donnelly, Neil; Swift, Wendy; Weatherburn, Don, "Driving under the influence of cannabis: The problem and potential countermeasures," Crime and Justice Bulletin, NSW Bureau of Crime Statistics and Research (Syndey, Australia: September 2005). p. 11.