About the survey: Conducted for the first time in 1973; repeated in 1986, 1996, 2007, and 2013-14; Collects data from 300 roadside sites across the country; Road signs alert drivers to a voluntary paid survey ahead; Strictly voluntary and anonymous; Drivers who are too impaired to safely drive from the research sites are offered other means to get home; of more than 30,000 participants over 40 years, none have driven away from the sites after being identified as impaired and none have been arrested; Testing for presence of illegal drugs, prescription medicines, and over-the-counter drugs conducted for the first time in 2007.