Citation

Porath-Waller AJ, Beirness DJ, Smither D. U.S. National Highway Traffic Safety Administration. Washington, D.C.: U.S. National Highway Traffic Safety Administration, 2021.

Copyright

(Copyright 2021, U.S. National Highway Traffic Safety Administration)

The full document is available online.

Abstract

The objective of this study was to determine which combinations of drug-related signs and symptoms from the Drug Evaluation and Classification (DEC) protocol most efficiently and effectively predict the drug category or combination used by the subject. A sample of 2,261 DEC evaluations conducted on suspected drug-impaired drivers was obtained from 11 States. The sample included cases that involved specific drug categories and two- drug combinations that are commonly encountered by DREs. To assess the signs and symptoms from the DEC evaluation that best predict the drug category or drug combination used by suspected drug-impaired drivers, a series of statistical analyses was conducted. This study also examined how effectively the set of drug-related measures from the DEC procedure could distinguish drug-positive from drug-negative cases for two common drug categories (cannabis and CNS depressants) and the relative importance of clinical, behavioral and observational measures in predicting drug categories responsible for impairment. Thirteen drug-related indicators were found to significantly contribute to the prediction of drug category; 12 indicators contributed significantly to the prediction of drug combinations. Additionally, indicators related to the appearance and physiological response of the eye contributed the most to the prediction of both single drug categories and drug combinations, followed closely by clinical indicators, and performance on the psychophysical tests. A qualitative analysis of cases ruled out for medical reasons revealed that the subjects were older than in other cases, were more likely to have been involved in a crash, and were more likely to report being diabetic. A variety of medical conditions and injuries were considered to have possibly influenced the evaluation or rendered the subject incapable of performing the tests.