The Detection of DWI at BACs below 0.10

Stuster, Jack, 1947- · 1997 · ROSA P / United States. National Highway Traffic Safety Administration

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Summary

This report documents a research project conducted for the National Highway Traffic Safety Administration (NHTSA) to identify behavioral cues associated with driving while impaired (DWI) at blood alcohol concentrations (BACs) below the traditional 0.10 limit. The study was motivated by the adoption of 0.08 BAC limits in 13 states and the need to update law enforcement training materials, which had previously relied on cues validated for the 0.10 threshold. The primary objective was to develop scientifically valid training materials to assist officers in accurately detecting impairment at lower BAC levels. The research was conducted in two phases involving 13 major tasks. Phase I included a comprehensive literature review, interviews with DWI experts, an analysis of approximately 1,000 low-BAC arrest reports, and two field studies. The first field study involved ride-along observations with police, while the preliminary field study collected data from over 12,000 enforcement stops across five agencies. Researchers recorded driving and post-stop cues for all stops, regardless of disposition, and obtained BAC readings for drivers exhibiting signs of alcohol consumption. Phase II involved a validation study with law enforcement agencies in 11 states with 0.08 limits. Officers used draft training materials and collected data on every enforcement stop to validate the identified cues. The results confirmed that the 20 driving cues from the original 1980 NHTSA guide remained valid predictors for BACs of 0.08 or higher. However, the study found no cues that reliably predicted BACs below 0.08; key predictors failed to emerge with useful probabilities at lower levels. The validation study further confirmed the original cues, added a few new driving cues, and established 10 post-stop cues. The final DWI detection guide categorized driving cues into four functional areas: Problems Maintaining Proper Lane Position, Speed and Braking Problems, Vigilance Problems, and Judgment Problems. Post-stop cues included difficulties with vehicle controls, balance issues, slurred speech, and providing incorrect information. The guide provided specific probability estimates for detecting DWI based on the presence of single or combined cues. The significance of this study lies in its provision of updated, evidence-based training materials for law enforcement. By validating cues for the 0.08 BAC limit, the report supports more effective DWI enforcement in jurisdictions with lower statutory limits. The findings clarify that while certain behaviors are strong indicators of impairment at 0.08, there are no reliable visual cues for detecting impairment at BACs below this threshold. This distinction helps officers make more accurate enforcement decisions, balancing the need to detect impaired drivers against the risk of false detections.

Key finding

The original NHTSA DWI detection guide cues remained effective for identifying impairment at the 0.08 BAC level, but no specific driving or post-stop cues were found to reliably predict BACs below 0.08.

Methodology

field_study

Sample size: 12000

Provenance

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

Topics

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• dui enforcement
• alcohol
• drowsy as impairment