Last updated : July 14, 2025
Researchers at the University of Colorado School of Medicine analyzed data collected by the National Highway Traffic Safety Administration and the results indicate there may be unintended consequences of legalizing marijuana in the state. NHTSA data from its Fatality Analysis Report System for years 1994 to 2011 was used and compared between states with and without legalized marijuana. Specifically, Colorado vehicle crashes were compared to crashes in 34 other states, with Colorado allowing medicinal use of marijuana at the time and the other states in the study with no medical marijuana laws at all. The 1994 baseline for all states, i.e., Colorado and the other 34 states, showed a similar marijuana influence on at least one driver involved in a two-vehicle accident. That level was at a 4.5% incidence level for the first half of the first year of data. Fatal crashes more than doubled by the second half of 2011 in Colorado, to a 10% level. The 34 states with no medicinal use saw no such percentage increase and as a “control” for the study, it was noted that presence of alcohol in drivers in fatal crashes was similar in all states during the time data was collected and analyzed.
Marijuana tied to more vehicle fatalities
The risk of motor vehicle crashes increases with marijuana use. Pot users are more likely to be involved in a motor vehicle accident by a factor of two if they drive within three hours of marijuana use. Although non-alcohol related accidents accounted for 11% of fatal accidents in Colorado, marijuana use accounted for the majority of accidents associated with substance abuse affecting motor vehicle fatalities.
Marijuana significant contributor to drug-impaired driving
The Colorado Department of Transportation reports that about a quarter of drivers positive for drug use were under the influence of marijuana in 2007. That marijuana incidence level climbed to 43% of drug positive drivers in 2008, 45% in 2009, and 58% in 2010. The implication is that more drug-positive drivers are “high” on marijuana versus other “recreational” drugs and that those percentages are increasing annually. Between 2007 and 2010 in excess of 16% of fatal car accidents involved drivers positive for drugs. Simple assessment might suggest that a little more than 4% of those accidents related to marijuana use in 2007 and as many as 9% of those same motor vehicle accidents related to the use of pot in 2010.
Cause and effect undetermined (but undeniable?)
Researchers were careful not to indicate a direct correlation drawn between legalizing marijuana and fatal crashes in Colorado, but the data does show that over that period of time (between 1994 and 2011 with medicinal use being approved by voters in 2000) marijuana users were more likely to be involved in fatal accidents than other chemical users and than non-users. Doctors suggest their findings concerning impaired driving may indicate the need for greater efforts to educate marijuana consumers and develop programs to minimize their impaired driving. Considering the data was collected before recreational use was legal in the state, it would appear that the study conclusion is correct.
