Drug and Alcohol Crash Risk: A Case-Control Study

Lacey, John H.; Kelley-Baker, Tara; Berning, Amy; Romano, Eduardo; Ramirez, Anthony; Yao, Julie; Moore, Christine; Brainard, Katharine; Carr, Katherine; Pell, Karen; Compton, Richard · 2016 · ROSA P / United States. National Highway Traffic Safety Administration. Office of Behavioral Safety Research

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Summary

This study addresses the quantification of crash risk associated with driving under the influence of alcohol, drugs, or both, a topic previously lacking comprehensive data in the United States due to reliance on self-report surveys or retrospective fatality analyses. The research was motivated by the need for rigorous, biologically verified evidence to inform public policy, similar to landmark studies that established alcohol-impaired driving laws. The primary objective was to estimate the relative crash risk for drivers testing positive for various substances using a controlled case-control design. The study employed a case-control methodology conducted over 20 months in Virginia Beach, Virginia. Researchers collected biological samples from more than 3,000 crash-involved drivers and 6,000 control drivers. To ensure precise matching, control drivers were recruited one week after each crash at the same location, time of day, day of week, and direction of travel. Data collection included 10,221 breath samples, 9,285 oral fluid samples, and 1,764 blood samples. Oral fluid and blood specimens were screened and confirmed for 89 drugs known to potentially affect driving ability. Statistical analysis utilized logistic regression to calculate unadjusted and adjusted odds ratios, controlling for variables such as age, gender, race/ethnicity, and alcohol concentration. The results identified alcohol as the largest contributor to crash risk. Drivers with a breath alcohol concentration (BrAC) of 0.05 g/210L were 2.07 times more likely to crash than sober drivers, while those at 0.08 g/210L were 3.93 times more likely. In contrast, after adjusting for demographic factors and alcohol use, no specific drug or drug class showed a statistically significant association with crash risk. The adjusted odds ratio for THC (marijuana) was 1.00, with similar non-significant findings for antidepressants, narcotic analgesics, sedatives, stimulants, and other medications. Furthermore, analyses found no significant interaction effects when drivers tested positive for both alcohol and drugs; in combined cases, alcohol alone accounted for the increased risk. The significance of these findings lies in the confirmation that alcohol is the primary substance-related risk factor for crashes in this dataset, while drugs did not independently contribute to crash risk after rigorous adjustment. The authors suggest this discrepancy with previous studies may stem from the inclusion of property-damage-only crashes, which are less severe than the fatal or serious injury crashes often studied elsewhere. Additionally, the long detection window of certain drugs like THC may result in positive tests for drivers who were no longer impaired. The study concludes that while drugs did not show statistical significance in this specific analysis, law enforcement should still consider the totality of circumstances when assessing impairment, as the study does not imply that driving after drug use is safe.

Key finding

After adjusting for age, gender, race, and alcohol consumption, no drug significantly contributed to crash risk, whereas alcohol remained the largest contributor with adjusted odds ratios of 2.07 at a BrAC of .05 g/210L and 3.93 at .08 g/210L.

Methodology

other

Sample size: 9000

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (45 acquisition events logged).

Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• illicit drugs
• polydrug
• cannabis
• alcohol
• induced exposure
• sex gender

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Empirical Findings: crash risk outcomes, observational prevalence
• Methodological Resource: dataset resource