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Highlights from the California Roadside Survey

Over 1,300 California drivers were randomly stopped on weekend nights and agreed to give alcohol breath tests and oral fluids for drug testing in nine cities across the state.  The survey was anonymous and voluntary.  The methods for the survey closely followed other roadside surveys, and a report is now available on the OTS website (Lacey, Kelley-Baker, Romano, Brainard, & Ramirez, 2012).  Drugs tested included illegal drugs as well as plausibly impairing medications.

Here are some of their main findings:

  • Drug-positive drivers made up about 1 in 7 drivers, a third of those drivers tested positive for more than one drug.
  • The percent of drivers testing positive for marijuana (7.4%) was almost identical to the percent testing positive for alcohol (7.3%).
  • About a quarter of marijuana-positive drivers also tested positive for another drug; about 13.3% marijuana-positive were also positive for alcohol.
  • Of those who admitted using marijuana more than once, only 22.4% said it had an effect on their driving; and third of those believed it improved their driving.  Thus, only 11% of the marijuana-experienced drivers believed it harmed their driving.  14.3% admitted to having driven within 2 hours of using marijuana in the past year.
  • There were more drivers (2.2% of the sample) who admitted taking medication that they think affected their driving than there were drivers who tested at or above .08 BAC (1% of drivers).
  • Of those who had recently used marijuana, about two-thirds reported smoking every day in the past month.
  • 3.7% of drivers had a medical marijuana permit and most of those drivers (65.8%) had used their permit to buy marijuana.

It is important to note that the marijuana tests performed included metabolites and thus do not necessarily reflect recent or impairing levels of THC.  The same issue actually arises with all of the drugs, in that only their presence and not the absolute level is reported.  Thus, it is not necessarily the case that drug-impaired driving is as prevalent as the drug-positive results reported.  Similarly for alcohol, most of the alcohol-positive results were BACs below .05 (62%). 

So this means… drugged driving is rightly emerging as an important public safety concern.  The rates of drug-positive drivers are at or above alcohol-positive drivers in high-risk weekend-night drivers.  Many drivers do not perceive any risk to driving following marijuana use. Concurrent use of marijuana with other drugs, medications and alcohol was found in many drivers.  These results mirror the Monitoring The Future data that demonstrate high school seniors were more likely to report marijuana-affected driving than heavy-alcohol driving (O’Malley & Johnston, 2007). Though research studies continue to sharpen our observations that marijuana and other drugs do result in increased crash risk (Grotenhermen et al., 2007), those most at risk for impaired driving are not yet getting the message.  


Grotenhermen, F., Leson, G., Berghaus, G., Drummer, O. H., Krüger, H.-P., Longo, M., … Tunbridge, R. (2007). Developing limits for driving under cannabis. Addiction, 102(12), 1910–1917.

Lacey, J., Kelley-Baker, T., Romano, E., Brainard, K., & Ramirez, A. (2012). Results of the 2012 California Roadside Survey of Nighttime Weekend Drivers’ Alcohol and Drug Use (p. 22). Calverton, MD: Pacific Institute for Research and Evaluation. Retrieved from

O’Malley, P. M., & Johnston, L. D. (2007). Drugs and driving by American high school seniors, 2001-2006. Journal of Studies on Alcohol and Drugs, 68(6), 834–842.