Driving, Drinking, and Drug Use
- Overview & Basic Data
- Estimates of Impairment & Risk
- Estimated DUID Prevalence
- Roadside Drug Testing Devices
- Other Specific Research Findings on Marijuana and Driving
- Laws & Policies
Page last updated June 10, 2020 by Doug McVay, Editor/Senior Policy Analyst.
6. Estimated Risk of Motor Vehicle Accident Associated With Marijuana Use
"This study of crash risk found a statistically significant increase in unadjusted crash risk for drivers who tested positive for use of illegal drugs (1.21 times), and THC specifically (1.25 times). However, analyses incorporating adjustments for age, gender, ethnicity, and alcohol concentration level did not show a significant increase in levels of crash risk associated with the presence of drugs. This finding indicates that these other variables (age, gender ethnicity and alcohol use) were highly correlated with drug use and account for much of the increased risk associated with the use of illegal drugs and with THC.
Compton, R. P. & Berning, A. (2015, February). Drug and alcohol crash risk. (Traffic Safety Facts Research Note, Report No. DOT HS 812 117). Washington, DC: National Highway Traffic Safety Administration, p. 8.
7. Estimated Risk Of Motor Vehicle Accident Associated With Marijuana Use
"Conducting case-control studies to estimate the risk of crash involvement from drug use presents many difficulties. The first challenge has been getting reliable and accurate estimates of drug use. Many studies rely on self-report (which have obvious inherent problems) rather than actual measurement of THC in blood or oral fluid.
Compton, R. P. & Berning, A. (2015, February). Drug and alcohol crash risk. (Traffic Safety Facts Research Note, Report No. DOT HS 812 117). Washington, DC: National Highway Traffic Safety Administration, pp. 1-2.
8. Odds Of Involvement In Fatal Auto Accidents Associated With Use Of Various Substances
"The prevalence of drugs detected in cases was higher than in controls across the drug categories (Table 3). Marijuana, narcotics, stimulants, and depressants were each associated with a significantly increased risk of fatal crash involvement, with estimated odds ratios ranging from 1.83 for marijuana to 4.83 for depressants (Table 3). Polydrug use, defined as use of two or more non-alcohol drugs, was associated with a 3.4-fold increased risk of fatal crash involvement (Table 3).
Guohua Li, Joanne E. Brady, and Qixuan Chen. Drug use and fatal motor vehicle crashes: A case-control study. Accident Analysis and Prevention 60 (2013) 205–210. http://dx.doi.org/10.1016/j.aa....
9. Cannabis Consumption, THC Levels, Performance Impairment
"It is difficult to establish a relationship between a person's THC blood or plasma concentration and performance impairing effects. Concentrations of parent drug and metabolite are very dependent on pattern of use as well as dose. THC concentrations typically peak during the act of smoking, while peak 11-OH THC concentrations occur approximately 9-23 minutes after the start of smoking. Concentrations of both analytes decline rapidly and are often < 5 ng/mL at 3 hours. Significant THC concentrations (7 to 18 ng/mL) are noted following even a single puff or hit of a marijuana cigarette. Peak plasma THC concentrations ranged from 46-188 ng/mL in 6 subjects after they smoked 8.8 mg THC over 10 minutes. Chronic users can have mean plasma levels of THC-COOH of 45 ng/mL, 12 hours after use; corresponding THC levels are, however, less than 1 ng/mL. Following oral administration, THC concentrations peak at 1-3 hours and are lower than after smoking. Dronabinol and THC-COOH are present in equal concentrations in plasma and concentrations peak at approximately 2-4 hours after dosing.
Couper, Fiona J., Logan, Barry K., et al., "Drugs and Human Performance Fact Sheets," (Washington, DC: National Highway Traffic Safety Administration, April 2004), pp. 8-9.
10. Medical Marijuana Laws Associated With Reduction in Traffic Fatalities
"Using population-based data from 1985 to 2014, we found that, first, states that enacted MMLs during the study period had lower fatality rates compared with states without MMLs. Second, on average, traffic fatalities further decreased in states post-MML, with both immediate (sudden change in fatality rate after MML enactment) and gradual (change in rate trend after MML enactment) declines over time in those aged 25 to 44 years. Third, the association between MML and traffic fatalities varied considerably across states. Fourth, the presence of operational dispensaries was also associated with reductions in traffic fatalities in those aged 25 to 44 years.
Julian Santaella-Tenorio, Christine M. Mauro, Melanie M. Wall, June H. Kim, Magdalena Cerdá, Katherine M. Keyes, Deborah S. Hasin, Sandro Galea, and Silvia S. Martins. US Traffic Fatalities, 1985–2014, and Their Relationship to Medical Marijuana Laws. American Journal of Public Health: February 2017, Vol. 107, No. 2, pp. 336-342.