Methodologies for Establishing the Relationship between Alcohol/Drug Use and Driving Impairment: Differences between Epidemiological, Experimental, and Real-Case Studies

A large proportion of road traffic crashes are caused by driver impairment after using alcohol or other psychoactive substances. This chapter describes the methodologies used to investigate the effect of alcohol and drugs on the ability to drive safely, presents the main advantages and challenges, and discusses disagreements between findings for some substances. Standardized research methods are needed in order to generate accurate and reproducible data when studying the effects of alcohol and drugs on the ability to drive safely. Analytical epidemiological studies involve comparing crash involvement among drivers who are using, versus not using, a substance that may potentially affect the ability to drive safely, or substance use among crash-involved versus non–crash-involved drivers. This may include cohort, case-crossover, case-control, and responsibility studies. The chapter also presents data from a selection of representative studies of alcohol, amphetamine/methamphetamine, cannabis, and diazepam.