An Examination of the Validity of the Standardized Field Sobriety Test in Detecting Drug Impairment Using Data from the Drug Evaluation and Classification Program

Abstract

Objective: The purpose of this study is to assess the validity of the 3 components of the Standardized Field Sobriety Test (SFST), including the Horizontal Gaze Nystagmus (HGN), One Leg Stand (OLS), and Walk and Turn (WAT) tests, in identifying impairment among suspected drug-impaired drivers using data recorded during drug evaluation and classification (DEC) evaluations.

Methods: Data from 2142 completed DEC evaluations of central nervous system (CNS) stimulants, CNS depressants, narcotic analgesics, cannabis, or no drugs were analyzed using multinomial logistic regression.

Results: All drug categories were significantly associated with impaired performance. On the HGN, users of CNS depressants were significantly more likely to experience lack of smooth pursuit and distinct nystagmus at maximum deviation compared to non-drug users. On the OLS, users of all drug classes were significantly more likely to sway while balancing and use their arms to maintain balance but significantly less likely to hop compared to drug-free cases. Users of CNS depressants, CNS stimulants, and narcotic analgesics were significantly more likely to put their raised foot down during the test. On the WAT, users of CNS depressants, CNS stimulants, and narcotic analgesics were significantly less likely to keep their balance while listening to test instructions compared to those who had not used drugs. Users of CNS depressants were less likely to touch heel-to-toe while walking, whereas individuals who had used narcotic analgesics were less likely to take the correct number of steps.

Conclusions: These findings provide support for the use of the SFST as a screening tool for law enforcement to identify impairment in persons who have used CNS stimulants, CNS depressants, cannabis, or narcotic analgesics.

Keywords:

• Standardized Field Sobriety Test (SFST)
• impairment testing
• impaired driving
• drugged driving
• Drug Evaluation and Classification (DEC) Program

Acknowledgments

The authors acknowledge the Royal Canadian Mounted Police for providing the data for this work.