"The recently published 2007 National Roadside Survey of Alcohol and Drug Use by Drivers: Drug Results reported the drug prevalence (detected by oral fluid and blood samples) in 7,719 weekend drivers who served as participants in the survey (Lacey et al., 2009). The prevalence of drugs in drivers tested during the daytime was 11%.1 Specifically, 5.8% tested positive for the category of illegal drugs, 4.8% for the medication category (i.e., prescription [Rx] and over-the-counter [OTC] medications), and 0.5% for the combined illegal and medication category. The nighttime survey results showed a prevalence of 14.4% for positive drug results. In this sample, 10.5% were positive for illegal drugs, 3% positive for the medication category, and 0.9% positive for the combined illegal and medication category. In addition, for those individuals who tested positive for illegal drugs (9.8%) the rate of those who also tested positive for alcohol was 28%. One of the major conclusions and recommendations of this study is that “further research is needed to determine the effect of drug prevalence on crash risk” (p.8)."


Kay, G. G., & Logan, B. K., (2011). Drugged Driving Expert Panel report: A consensus protocol for assessing the potential of drugs to impair driving. (DOT HS 811 438). Washington, DC: National Highway Traffic Safety Administration, p. 1.