Results of the 2013–2014 National Roadside Study of Alcohol and Drug Use by Drivers [Traffic Safety Facts]
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Summary
This report presents the findings of the 2013–2014 National Roadside Survey (NRS) of Alcohol and Drug Use by Drivers, conducted by the National Highway Traffic Safety Administration (NHTSA). The study aims to estimate national prevalence rates of alcohol and drug use among drivers, building upon a series of surveys dating back to 1973. While previous surveys focused primarily on breath alcohol concentration (BrAC), the 2007 and 2013–2014 surveys incorporated toxicological testing for potentially impairing drugs, including illegal substances and legal medications. This expansion allows for the first national-scale examination of trends in drug use among drivers. The methodology involved a multistage sampling procedure across 60 sites in the contiguous United States, representing various regions and population densities. Data were collected from voluntary, anonymous participants during two distinct periods: weekday daytime hours (Friday) and weekend nighttime hours (Friday and Saturday nights). Drivers provided breath, oral fluid, and blood samples. Of the 11,100 eligible drivers, 85.2% provided breath samples, 71.0% provided oral fluid samples, and 42.2% provided blood samples. National prevalence rates were calculated using a weighting scheme based on crash volume and selection probability. The results indicate a significant long-term decline in alcohol use. The percentage of weekend nighttime drivers with any detectable alcohol decreased from 35.9% in 1973 to 8.3% in 2013–2014. Specifically, the proportion of drivers with illegal BrAC levels (≥ .08 g/210 L) dropped from 7.5% to 1.5%, an 80% reduction. Alcohol use was significantly higher during weekend nights (8.3% positive) compared to weekday days (1.1% positive). In contrast, drug prevalence did not vary significantly by time of day, with approximately 22% of drivers testing positive for drugs in both periods. However, the type of drug varied by time: illegal drug use increased from daytime (12.1%) to nighttime (15.2%), while medication use decreased from daytime (10.3%) to nighttime (6.9%). Comparing 2013–2014 data to 2007 using consistent cutoffs, illegal drug prevalence among weekend nighttime drivers rose from 12.4% to 15.1%, driven largely by a 48% increase in THC positivity (from 8.6% to 12.6%). The study concludes that while alcohol-impaired driving has decreased substantially, drug use among drivers is rising, particularly regarding marijuana. The authors emphasize that unlike alcohol, there is no established correlation between drug concentrations and driver impairment due to factors such as individual metabolism, tolerance, and detection windows. Consequently, the presence of drugs in biological samples does not necessarily indicate current impairment. The findings suggest that changes in state marijuana policies may be contributing to increased THC prevalence, warranting continued monitoring.
Key finding
The percentage of weekend nighttime drivers with a blood alcohol concentration of 0.08 or higher decreased from 7.5 percent in 1973 to 1.5 percent in 2013–2014, while the prevalence of drug-positive drivers increased from 16.3 percent in 2007 to 20.0 percent in 2013–2014.
Methodology
on_road
Sample size: 11100
Provenance
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
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| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 3 | 2026-06-10 |
| tag | success | vector_similarity | — | — | 19 | 2026-06-11 |
| verify | success | — | — | — | 2 | 2026-06-10 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.
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- Empirical Findings: observational prevalence