Random tests of U.S. drivers revealed that fewer Americans are driving drunk, but more have traces of illicit drugs in their bodies, the New York Times reported July 13.

The report from the National Highway Traffic Safety Administration (NHTSA), based on blood, breath and saliva tests collected on weekends from drivers in 300 locations nationally, found that just 2.2 percent had blood-alcohol levels in excess of the legal limit of .08 percent. In 1973, 7.5 percent of drivers similarly tested had blood-alcohol levels of .08 percent or higher.

Men were more likely to be driving drunk than women, and most impairment was detected between the hours of 1 a.m. and 3 a.m. Motorcyclists and pickup-truck drivers were more likely to be intoxicated than drivers of other vehicles.

NHTSA researchers also found that 16.3 percent of drivers had detectable traces of marijuana (9 percent), cocaine (4 percent) or prescription drugs (4 percent) in their system. However, unlike with alcohol, the drug tests do not necessarily indicate recent drug use or impairment.

The voluntary, anonymous study was conducted by volunteers, not police. Drunk drivers faced no sanctions but were not allowed to drive home. About 11,000 drivers were included in the study; participants were rewarded with cash payments of $10 for saliva samples, $50 for blood samples, and $100 if they initially refused to be tested.