Field Evaluation of the Los Angeles Police Department Drug Detection Procedure

NHTSA · 1986 · ROSA P / United States. National Highway Traffic Safety Administration

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Summary

This 1986 National Highway Traffic Safety Administration (NHTSA) report evaluates the accuracy of the Los Angeles Police Department’s (LAPD) Drug Recognition Expert (DRE) procedure. The study was motivated by the lack of validated tools for law enforcement to identify drug-impaired drivers, particularly when alcohol was not the primary cause of impairment. While a prior laboratory study showed promising results, this field evaluation aimed to validate the procedure under real-world conditions with a wider range of officers and suspects. The study involved 219 suspects arrested for driving under the influence (DUI) in Los Angeles between June and September 1985. Twenty-five senior DREs evaluated suspects at two central jail facilities using a standardized procedure comprising interviews, physiological symptom checks (e.g., pupil size, pulse, nystagmus), and behavioral tests (e.g., Romberg balance, walk-and-turn). Blood samples were obtained from 173 suspects (86% of those judged impaired by drugs) and analyzed for amphetamines, barbiturates, cocaine, cannabinoids, opiates, PCP, benzodiazepines, and alcohol. Suspects judged not to be under the influence of drugs were excluded from blood testing, meaning the study could not assess the rate of false negatives. The results demonstrated high accuracy in detecting the presence of drugs. When DREs claimed drugs other than alcohol were present, they were confirmed in the blood 94% of the time. DREs correctly identified at least one drug in 87% of cases. However, identifying specific drug classes was less precise; when a DRE identified a specific drug, it was detected in the blood 79% of the time. Multiple drug use was prevalent, with 72% of suspects having two or more substances in their blood. PCP was the most frequently detected drug (56%), followed by alcohol (52.6%) and marijuana (44.5%). Accuracy decreased as the number of drugs present increased; DREs were entirely correct in 53% of single-drug cases but only 25% of cases involving three drugs. The study concludes that the LAPD DRE procedure is a reliable tool for determining whether a driver is impaired by drugs other than alcohol and for identifying the general presence of such substances. However, the procedure’s ability to pinpoint specific drug classes is compromised by the high frequency of polydrug use among impaired drivers. The findings support the validity of the DRE program for law enforcement purposes, though they highlight the complexity of diagnosing specific drug impairment in field settings.

Key finding

Drug Recognition Experts correctly identified the presence of non-alcohol drugs in suspects' blood 94% of the time and accurately identified at least one specific drug in 87% of cases.

Methodology

field_study

Sample size: 173

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
• dui enforcement
• polydrug