Understanding the Limitations of Drug Test Information, Reporting, and Testing Practices in Fatal Crashes [Traffic Safety Facts]: Research Note

Berning, Amy; Smither, Dereece D. · 2014 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This research note by Berning and Smither (2014) addresses the critical limitations inherent in the Fatality Analysis Reporting System (FARS) data regarding drug-involved driving in fatal crashes. While the National Highway Traffic Safety Administration (NHTSA) has collected comprehensive data on fatal crashes since 1975, the interpretation of drug-related variables is significantly more complex than alcohol-related data. Unlike blood alcohol concentration (BAC) data, which utilizes statistical imputation for missing values, drug data in FARS lacks estimates for missing information or impairment levels. The paper aims to clarify these complexities to prevent misinterpretation of drug presence as drug impairment and to highlight inconsistencies in testing and reporting practices across jurisdictions. The authors analyze data from 2008 to 2012, examining the distinction between drug presence and impairment. A key finding is that FARS data indicates only whether a drug was present in a driver’s system, not whether the driver was impaired. For instance, cannabinoids can be detected weeks after use, meaning a positive test does not necessarily correlate with impairment at the time of the crash. Furthermore, there are no universally accepted impairment thresholds for drugs comparable to the 0.08 g/dL BAC standard for alcohol. The study highlights significant procedural variations across states, including differences in who is tested (e.g., only fatally injured drivers vs. all drivers), the types of drugs screened, biological specimens used, and laboratory cut-off levels. These inconsistencies mean that jurisdictions with higher testing rates or broader drug panels naturally report higher percentages of drug-positive drivers, confounding cross-state and temporal comparisons. Data analysis reveals that the majority of drivers involved in fatal crashes were not tested for drugs; only 41% in 2008 and 40% in 2012 were tested. Among those tested, the percentage of drug-positive results appeared to increase from 26% in 2008 to 32% in 2012. However, the authors caution that this trend cannot be interpreted as an increase in drugged driving. Instead, it likely reflects increased testing rates, lower testing costs, and broader drug panels. Additionally, reporting inconsistencies exist, with some laboratories failing to submit results to FARS and the database having limited capacity to record multiple drug findings or metabolites. The significance of this work lies in its warning against drawing causal inferences from current FARS drug data. The authors conclude that the data is insufficient for comparing drug use across years or states, nor can it reliably determine crash causation or impairment levels. Users of FARS data must account for these methodological limitations, including the distinction between presence and impairment and the lack of uniform testing protocols. The paper underscores the need for more complete and standardized data collection to strengthen future analyses of drug-involved driving.

Key finding

FARS data indicates drug presence rather than impairment, and inconsistent testing protocols across jurisdictions prevent valid comparisons of drugged driving trends or causation.

Methodology

dataset

Provenance

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

Topics

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• illicit drugs
• cannabis
• polydrug
• dui enforcement

Information type

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• Empirical Findings: crash risk outcomes, observational prevalence