The number of road traffic deaths worldwide continues to rise steadily reaching 1.35 million persons in 2016, up to about 50 million people are injured in road traffic crashes (RTCs). The number of RTC fatalities is decreasing in high-income countries but significantly increasing in low- and middle-income countries. Driving under the influence (DUI) of alcohol has for many years been well known as a risk for road traffic safety. Systematic studies of drug use among suspected drug-impaired drivers and drivers killed in RTCs have been performed since the late 1980s. The first studies on the prevalence of drugs among random drivers were performed in Australia and Germany in the 1990s. The prevalence of alcohol and other substances among drivers involved in RTCs gives valuable information of the association between DUI and RTC, and data on alcohol and drug trends among drivers and possible effects after changes in law and enforcement.