Executive Summary
The Pacific Institute for Research and Evaluation (PIRE) worked with the National Highway Traffic Safety Administration (NHTSA) to develop and conduct a “Pilot Test of New Roadside Survey Methodology for Impaired Driving.” This final report presents the results of the two phases of the project:
(1) The feasibility study, in which the procedure to collect survey data and biological samples at the roadside was developed and refined; and
(2) The pilot test, in which the developed procedure was tested in six States.
This study lays the groundwork for the next decennial national roadside survey of impaired driving, which will estimate the incidence of alcohol- and drug-positive drivers on U.S. roads.
Background
Three prior national roadside surveys of drivers have been conducted. The first, sponsored by NHTSA, was in 1973 (Wolfe, 1974). The second, sponsored by the Insurance Institute for Highway Safety (IIHS), was in 1986 (Lund & Wolfe, 1991). The most recent, in 1996, was funded by NHTSA and IIHS (Voas et al., 1998). These surveys were taken of a national probability sample from the 48 contiguous States.
New to this pilot test was to develop and test the collection of additional types of biological samples which could be used to determine the extent of the presence of drugs other than alcohol in the nighttime driving population. These data are essential to developing more precise estimates of the crash risk associated with the presence of alcohol and other drugs in drivers and measuring the national progress in reducing the prevalence of alcohol- and drug-impaired driving. The full-scale roadside survey will be more extensive than any previous project, and will provide a much broader perspective on which drugs are detected in the nighttime driving population than previously known.
Methodology
In the feasibility study, PIRE developed and tested a roadside survey protocol for (1) subject sampling, (2) sample collection and analysis, and (3) data presentation. We collected data (survey, breath, oral fluid, and blood) from approximately 50 drivers in Delaware. This provided preliminary indications of the potential ability to assess the incidence of alcohol- and other drug-positive drivers in the nighttime driving population, and provided data on alcohol use from breath samples, and alcohol and other drug use from oral fluid (saliva) samples. Additionally, we examined the feasibility of obtaining blood samples from drivers. We also developed and tested a screening instrument designed to detect alcohol use disorders (AUDs) among the nighttime driving population. This activity was funded through a grant from the National Institute of Alcohol Abuse and Alcoholism (NIAAA).
After the feasibility test and procedure development, PIRE conducted a pilot test to refine data collection procedures and test analytic procedures. In the pilot study, we collected data (breath, oral fluid, and blood) from approximately 100 drivers at each of six sites across the country (for a target total of at least 600 subjects providing oral fluid samples). These sites were selected from the primary sampling units of the National Analysis Sampling System (NASS) of NHTSA. Thus, the pilot test was 1/10 of the contemplated sample size of the next national roadside survey (6,000 subjects), which will be used to estimate the incidence of alcohol and drugged driving on our Nation’s roadways. The intent of this Pilot Test was to develop and test procedures that would be used in the next full-scale national roadside survey. It was not designed to yield a nationally-representative sample of the nighttime weekend driving population; thus the results are not representative of the United States as a whole.
Conclusion
One use of the national roadside survey is to track trends in alcohol levels of the nighttime driving population. Though this study is a pilot test and the sample size is relatively small, it is of interest to examine the general results in relation to previous national roadside surveys. These are presented in the figure below (Figure 1) and are generally quite encouraging. The long-term trend has been for an ever increasing proportion of survey respondents to have zero blood alcohol concentration (BAC) readings and for fewer to have positive readings at each level of BAC reading. That seems to have held true in this pilot test, conducted nearly a decade after the most recent national roadside survey. However, because of the small sample size in the pilot study, one cannot say definitively that that is the true trend. Such conclusions are best left for the next full-scale national roadside survey.
Figure 1. BACs of Drivers in National Surveys
The major focus of this study was to determine whether it is feasible and practical to collect oral fluid and blood from the nighttime driving population and analyze them for drugs. We determined that it is feasible to do so, with a lower response rate than that achieved for breath tests of alcohol. However, one should bear in mind that the overall response rates achieved (67% for oral fluid and 42% for blood) are in line with many telephone and mail surveys, which of course are based on self-report. Results of the analyses of the specimens obtained indicated that approximately 16 percent of these nighttime drivers tested positive for drugs other than alcohol. Additionally, the results of the chemical analyses indicated a much higher use rate than that obtained for the same subjects based on self-report. The most frequently encountered drug was marijuana and its metabolites, followed by cocaine and amphetamines. Another area examined was whether it was feasible and practical to administer a brief alcohol use disorder (AUD) self-report screening instrument at the roadside. Again we found that this was feasible and meaningful results could be obtained.
In summary, the results of this pilot test indicate that it is practical to expand the traditional roadside survey to include self-report based measures of AUD and biological measures of drug use. The objective biological measures, either through oral fluid or blood, are much to be desired over reliance on self-report of drug use.