The trend for driving after using marijuana was curvilinear, decreasing in the early years, then increasing in recent years; these results are consistent with trends in use of marijuana.21 The trend for driving after using illicit drugs other than marijuana was essentially flat. The trend for driving after drinking any alcohol or 5 or more drinks was downward, again consistent with overall trends in those behaviors. The final measure, which combined use of illicit drugs and heavy drinking, reflected all these trends. The trends for being a passenger in a car with a driver who had used drugs or drunk alcohol followed similar patterns, as did the combination of driving and riding data.
Some of the percentages were disturbingly large: for example, more than a quarter (28%) of the class of 2011 reported that at least once in the past 2 weeks they were the driver or a passenger in a car when the driver had used marijuana or another illicit drug or had had 5 or more drinks. This measure had an even higher value in the class of 2001 (32%; difference significant at P