Driving After Drug or Alcohol Use Report fnldrft.htm

In an effort to address the lack of available data on drug use and driving, this report contains findings from questions included in the 1996 National Household Survey on Drug Abuse (NHSDA). The data presented describe the prevalence and patterns of driving following drug and/or alcohol use by 11,847 NHSDA respondents, representing over 166 million persons age 16 and older who drove in the past year and also answered the question on driving after substance use. The data provide a demographic and behavioral profile of individuals who reported driving after drug use that may be used to guide the development of appropriate prevention and intervention measures. This chapter summarizes the major findings and briefly notes some policy implications.

In the year prior to their interviews, approximately 9 million people, or 5 percent of drivers, reported driving within two hours after drug use. About 45 million people, or 27 percent of drivers, drove within two hours after alcohol use. About 7 million people, or four percent of drivers drove after both alcohol and drug use (not necessarily concurrently). Marijuana was by far the most commonly used drug by those who drove after drug use. About four percent of drivers reported driving after marijuana use; one percent or less of drivers reported driving following each of the other drugs examined (i.e., cocaine, tranquilizers, stimulants, and sedatives).

Although the majority of both those who drove after drug use and those who drove after alcohol use were age 21-49, the prevalence of driving after drug use was highest among drivers age 16-20. By contrast, driving after alcohol use was more common among drivers age 21-49, particularly for non-Hispanic whites. Both behaviors were much less common among drivers age 50 and older.

Even though driving after drug use was more common among drivers age 16-20 than among drivers age 21 and older, the driving patterns of those who drove after marijuana use were similar for both age groups. The majority of those who drove after marijuana use were heavy marijuana users, having driven after marijuana use on at least one occasion in the past month. Regardless of the driver’s age, the majority of driving following marijuana use occurred in urban areas, on smaller roads, on weekends, and between the hours of 6:00 p.m. and 6:00 a.m. In addition, drivers most commonly reported that they had "no other way to get there" or were "not high enough to cause a crash" on their most recent occasion of driving after marijuana use. Drivers generally felt that marijuana did not affect their ability to drive and that they were no more likely to be stopped by the police when driving after marijuana use than when driving on other occasions. Drivers age 16-20 were most likely driving from a friend or relative’s home to their own home on their most recent occasion of driving after marijuana use. Drivers age 16-20 were also more likely to use marijuana alone or in combination with other drugs, while drivers age 21 and older were more likely to use marijuana in combination with alcohol.

Driving after alcohol use was more common among drivers age 21 and older and these drivers also reported driving after alcohol use on more occasions in the past month than drivers age 16-20. However, the younger drivers were more likely to report heavy alcohol use. In addition, drivers age 16-20 were more likely to report having consumed larger amounts of alcohol in a shorter period of time on their most recent occasion of driving following alcohol use. As a result of heavier alcohol use, drivers age 16-20 also had substantially higher average estimated blood alcohol concentration (BAC) levels than drivers age 21 and older, indicating a higher level of impairment.

Consistent with the finding that driving after drug use was more common among drivers age 16-20, these drivers were also more likely to have been never married and to have annual personal incomes less than $10,000. In contrast, driving after alcohol use was more common among those who were married and had an annual personal income of $50,000 or more. The latter finding may also be related to the fact that driving after drug use was more common among unemployed drivers, while driving after alcohol use was more common among those who were working full-time.

Males were substantially more likely than females, regardless of race/ethnicity, to drive after drug and/or alcohol use. This gender difference was especially large for Hispanics. For those who drove after alcohol use, the gender difference was greater among drivers age 21 and older than among drivers age 16-20. However, there was a tendency for female drivers age 25 and older to have higher average estimated BAC levels than males of the same age.

Drivers who had been arrested or who were on probation in the past year were more likely to report driving after drug and/or alcohol use. Driving after alcohol use was equally common among those with and without this criminal justice involvement.

Many of these findings have practical and policy implications. For example, those who reported driving after marijuana use generally did not feel that this use impaired their driving ability. This finding suggests the need to develop targeted drug awareness education programs that highlight the physiological effects of marijuana use.

The section of this report on estimated BAC levels also contains important policy-relevant findings. For example, despite the presence of zero tolerance laws for drivers under age 21, when drivers age 16-20 drive after alcohol use they are likely to have estimated BAC levels higher than .08 g/dl (the legal limit for drivers age 21 and older in some states). Given this finding, and also given the fact that drug use and driving is more common among drivers age 16-20, age-appropriate prevention and intervention measures should be developed to specifically target this age group, particularly the heavy drug and alcohol users.

Females over age 25 had higher estimated BAC levels than males of the same age. This finding may indicate lack of knowledge among females about the differential physiological effects of alcohol on women. Therefore, even though driving after substance use is substantially more common among males, prevention and intervention measures should address gender differences in the physiological response to alcohol.

As noted in Chapter 1, there are some limitations to these data that should be considered in interpreting the results. First, the data are entirely self-reported and may be under or over-reported. Second, the reported occurrence of driving following drug use was relatively uncommon relative to driving following alcohol use; therefore, the analysis of this behavior is based on a substantially smaller sample size than that for driving following alcohol use. Results should be interpreted with this in mind. Third, even though BAC levels were calculated to serve as a proxy for level of alcohol impairment, there is no true indicator for the level of driver impairment, particularly following drug use. Furthermore, even though the legal BAC limit is currently .08 g/dl in 16 states, research suggests that there can be significant impairment in driving-related skills at BAC levels as low as .02 g/dl (IIHS, 1995; NHTSA, 1988; NHTSA, 1992a). Therefore, comparisons of estimated BAC levels to legal BAC levels serves primarily as an indication of the prevalence of illegal behavior. Finally, this report is an analysis of every reported instance of driving following drug and/or alcohol use, regardless of the amount of the substance consumed. A more detailed examination of the average quantity of these substances consumed prior to driving would aid the development effective policies and prevention and intervention programs.

SAMHSA, an agency in the Department of Health and Human Services, is the Federal Government's lead agency for improving the quality and availability of substance abuse prevention, addiction treatment, and mental health services in the United States.

* Adobe™ PDF and MS Office™ formatted files require software viewer programs to properly read them. Click here to download these FREE programs now

CHAPTER 3: CONCLUSIONS