"The 2007 NRS found a dramatic decline in the number of drinking drivers with BACs [Blood Alcohol Content] at or above the current legal limit of 0.08 g/dL* on weekend nights compared to previous surveys (Figure 1). In 1973, 7.5% of drivers NHTSA’s National Center for Statistics and Analysis had BACs at or above 0.08 g/dL. In 2007, there were only 2.2% of drivers with a BAC at or above the current legal limit. This represents a decline of 71% in the percentage of alcohol-impaired drivers on the road on weekend nights. Similar declines were found at other BAC levels. For example, the percentage of drinking drivers (any positive BAC) declined almost as much over this time period, but one cannot infer impairment at very low BACs."


Compton, Richard and Berning, Amy, "Results of the 2007 National Roadside Survey of Alcohol and Drug Use by Drivers" (Washington, DC: Dept. of Transportation, National Highway Traffic Safety Administration, July 2009), DOT HS 811 175, p. 1.