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Sobriety tests for low blood alcohol concentrations
A James McKnight1, Elizabeth A Langston, A Scott McKnight
1Pacific Institute for Research and Evaluation, Calverton, MD 20705-3201, USA. jimmcknight@earthlink.net
Accident; Analysis and Prevention
|April 10, 2002
Summary
Detecting impaired drivers at lower blood alcohol concentrations (BAC) requires reliable field tests. Horizontal gaze nystagmus (HGN) from the standardized field sobriety test (SFST) effectively identifies drivers with BACs between 0.04% and 0.08%.
Area of Science:
- Forensic Toxicology
- Traffic Safety Research
- Neuroscience
Background:
- Legal blood alcohol concentration (BAC) limits for commercial and underage drivers are stricter than for other drivers.
- Effective, easily administered field sobriety tests are needed to establish probable cause for breathalyzer tests at lower BAC levels.
Purpose of the Study:
- To evaluate the efficacy of various performance and appearance measures in distinguishing BACs below and above 0.04% within the 0.00-0.08% range.
- To identify reliable indicators of low-level alcohol impairment for law enforcement.
Main Methods:
- Controlled experiments were conducted with alcohol-dosed subjects.
- Measures of heat loss, pupillary response, balance, complex tasks, and accuracy under speed were assessed.
- Horizontal gaze nystagmus (HGN) was administered using standardized field sobriety test (SFST) criteria with alternative scoring.
Main Results:
- Horizontal gaze nystagmus (HGN) was the only reliable index of blood alcohol concentration (BAC) in the 0.00-0.08% range.
- While other measures showed individual changes, inter-individual differences limited their utility for detecting BACs below 0.08%.
- HGN demonstrated validity in detecting BACs between 0.04% and 0.08%, comparable to its effectiveness at higher BACs.
Conclusions:
- Horizontal gaze nystagmus (HGN) is a valid and reliable indicator for detecting drivers with BACs in the 0.04-0.08% range.
- HGN testing is effective whether the subject is seated or standing, offering practical benefits for law enforcement.
- The findings support the use of HGN as a critical tool for establishing probable cause in impaired driving investigations, especially at lower BAC levels.