This report summarizes the results of a feasibility study and pilot study conducted by the Pacific Institute for Research and Evaluation (PIRE) under the National Highway Traffic Safety Administration (NHTSA) Task Order “Pilot Test of New Roadside Survey Methodology for Impaired Driving” under Contract DTNH22-02-D-95121.


Three prior national roadside surveys of drivers have been conducted in the United States. 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.

Historically, a roadside survey in the context of this study has been a survey conducted during weekend nights where drivers are stopped at random, a brief interview is conducted and a breath sample is requested in order to determine the drivers’ blood alcohol concentration (BAC). These surveys have been used to track progress in the Nation’s effort to reduce alcohol-impaired driving.

In 1996, breath samples were requested from 6,298 drivers, of which 95.7 percent provided a valid breath sample. In 1986, 93.7 percent of 3,043 drivers provided a breath sample and in 1973, 86.3 percent of 3,698 drivers did so. In the 1996 survey, 17 percent of nighttime weekend drivers had a positive breath alcohol concentration (BAC), compared to 26 percent in 1986, and 36 percent in 1973. In 1996, there was a significant decrease in drivers with BACs of .05 or below compared to 1986, but little or no change in drivers with higher BACs. There was also a significant decrease in drivers under the age of 21 who had been drinking heavily (greater than .10 BAC) in 1996 compared to the previous surveys (4% in 1973 to .3% in 1996) (see Table 1).

Table 1. Trends From Prior National Roadside Surveys









Breath Samples




Positive BAC




<21 Yrs. BAC >.10




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 additional data are essential to estimating the national progress in reducing the prevalence of alcohol- and drug-impaired driving. Another aspect of this pilot study was to develop and pilot test a self-report screening instrument to determine alcohol use disorder (AUD) prevalence in the nighttime driving population. This activity was funded through a grant from the National Institute of Alcohol Abuse and Alcoholism (NIAAA). 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. This pilot study is intended to both develop data collection and analysis techniques for biological samples other than breath and to test the viability of those techniques in the context of previous roadside survey sampling procedures.

Drug Testing Opportunities

Typically, previous national roadside surveys used an off-duty police officer to randomly stop nighttime weekend drivers so that researchers could ask them a few questions about their driving and drinking, and then obtain a breath test as an objective measure of their BAC. However, since the first national roadside survey was conducted, the technology for collecting and analyzing oral fluid or saliva to detect drugs (including alcohol) has greatly improved. Oral fluid testing for recent use of alcohol and other drugs of interest appears to be a promising method for testing drivers for drugs other than alcohol in the upcoming full-scale national roadside survey.

In a recent study conducted by Cone et al. (2002), oral fluid testing of 77,218 subjects in private industry showed a 5 percent positive rate for any the five Substance Abuse and Mental Health Services Administration (SAMHSA) drug categories (marijuana, cocaine, opiates, phencyclidine, and amphetamines). The pattern and frequency of drug positives was remarkably similar to urine drug prevalence rates in the general workplace from other surveys (Cone et al., 2002). Further, in a study of 180 drivers given blood, urine, and oral fluid tests which were analyzed using quantitative Gas Chromatography/Mass Spectrometry (GC/MS), the positive predictive value of oral fluids was 98 percent for amphetamines, 92 percent for cocaine, and 90 percent for cannabinoids (Samyn et al., 2002).

However, in an analysis of blood, urine, saliva, and sweat from 198 injured drivers admitted to a hospital, saliva detected only 14 positives for cannabinoids, while 22 positives were detected in the urine. The amount of matrix (body fluid) collected in saliva appears to be smaller when compared to urine, and the levels of drugs are typically higher in urine than in saliva, according to the authors (Kintz et al., 2000). In a study of saliva and sweat, Samyn and van Haeren (2000) concluded that saliva should be considered a useful analytical matrix for the detection of drugs of abuse after “recent use” when analyzed using GC/MS. This finding is most desirable in the roadside testing of drivers.

Yacoubian et al. (2001), tested 114 adult arrestees using saliva and urine and concluded that saliva testing may have certain advantages over urine testing for drugs, including (1) ease of sample collection, (2) subject preference for giving saliva over urine, (3) less vulnerability of adulteration in saliva, (4) little concern for subjects producing an adequate sample with saliva, and (5) saliva storage is easier than urine. The authors found a sensitivity of 100 percent and a specificity1 of 99 percent for cocaine in saliva and a sensitivity of 88 percent and specificity of 100 percent for heroin. However, saliva results only had a sensitivity of 5 percent for marijuana, likely reflecting only detection of very recent smoking, in that marijuana does not migrate from the blood supply to the oral fluid. Thus, positives in oral fluid are an indication of residual marijuana remaining in the mouth after ingestion. This may well be a positive factor for the current study in that when marijuana is detected in saliva, it is more likely to be in its active phase in the body rather than simply evidence the marijuana has been consumed during a look-back period which may be as long as two weeks and may no longer have a potential impairing effect.

Hold et al. (1999) conducted a review of the literature of using saliva for drug testing; the review included 135 references and provided guidelines for techniques for collecting and measuring drugs in saliva. In an earlier review of drugs of abuse found in saliva, Schramm et al. (1992) concluded that initial studies with cocaine and phencyclidine suggested a correlation between saliva and blood concentration, but that tetrahydrocannabinol (THC) does not appear to be transferred from blood to saliva. Recent marijuana smoking, however, can be detected in saliva from the buccal cavity.2

With regard to saliva and BAC, Bates et al. (1993), found that saliva strips and breath tester results for alcohol correlated very highly (r=.89-.90) with each other. Blood sample analyses, however, still remain the “gold standard” in terms of measurement of alcohol and other drugs in the human body, because they are the form of analysis which has been most established.

Project Objectives

This study was composed of two main components—a feasibility study and a pilot study.

In the feasibility study, PIRE developed and tested the protocol for (1) driver sampling, (2) sample collection and analysis, and (3) data presentation for a roadside survey incorporating collection of oral fluid and blood.

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 (600 subjects). These sites were selected from the primary sampling units of the National Automotive Sampling System/Crashworthiness Data System (NASS/CDS) 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.  On the following pages we describe the activities undertaken to conduct the pilot test, present the results of that endeavor and discuss issues that should be addressed in preparation for the full-scale national roadside survey.


1 Sensitivity: Sensitivity is ability of a test to measure what it purports to measure or in this case the ability of the oral fluid tests to correctly identify active drug users.  It is operationalized as a proportion represented by the true positives (i.e., those who are drug positive and actually test positive) divided by all persons who are drug positive [i.e., those who are positive and test positive (i.e., true positives) plus those who are positive and test negative (false negatives)]. The formula for sensitivity is Sn = TP / (TP + FN) where TP and FN are the number of true positive and false negative results, respectively. You can think of sensitivity as 1 minus the false negative rate. Notice that the denominator for sensitivity is the number of drug positive persons.
Specificity: Specificity is the ability of a test to correctly identify non-cases of disease or in this case the ability of the oral fluid tests to correctly identify non-drug users.  It is operationalized as a proportion represented by the true negatives (i.e., those who are drug negative and test negative) divided by all persons who are drug negative [i.e., those who are negative and test negative (i.e., true negatives) plus those who are negative, but falsely test positive (false positives)]. The formula for specificity is Sp = TN / (TN + FP) where TN and FP and the number of true negative and false positive results, respectively. You can think of specificity as 1 minus the false positive rate. Notice that the denominator for specificity is the number of non drug users.

2 The buccal cavity includes that part of the mouth bounded anteriorly and laterally by the lips and the cheeks, posteriorly and medially by the teeth and/or gums, and above and below by the reflections of the mucosa from the lips and cheeks to the gums.