Field sobriety tests (FSTs) are a key part of DWI investigations. Law enforcement officers use them to assess a driver’s potential impairment. These assessments are subjective and potentially unreliable, evaluating balance, coordination, and capacity to adhere to instructions; a multitude of factors can compromise their accuracy.
What are field sobriety tests?
FSTs are a series of physical and mental exercises that an officer requires a driver to perform. The results of these tests, with other observations, justify a DWI arrest. The National Highway Traffic Safety Administration (NHTSA) has standardized three primary tests, but their validity is frequently questioned.
Horizontal gaze nystagmus (HGN) test
The horizontal gaze nystagmus test assesses involuntary eye movement (nystagmus) as a driver follows a moving object. While officers assert this indicates impairment, numerous medical conditions and other factors can elicit nystagmus. Consequently, the test’s accuracy heavily depends on the officer’s administration and interpretation, both of which may be flawed.
Walk-and-turn test
The walk-and-turn test evaluates a person’s ability to follow directions and maintain balance. The officer instructs the driver to take nine heel-to-toe steps along a straight line, turn, and take nine steps back. Nevertheless, factors such as uneven surfaces, inadequate lighting, or a person’s natural coordination can adversely affect performance. An officer’s subjective judgment of “failure” can be challenged.
One-leg stand test
The one-leg stand test assesses an individual’s balance and ability to follow instructions. The officer requires the driver to stand on one leg, with the other leg raised, and count aloud. This test is subject to numerous variables, including age, weight, injuries, and footwear, all of which can compromise balance.
Field sobriety test results can face challenges in several ways, including arguments about incorrect administration, inaccurate officer observations, or the influence of extraneous factors such as medical conditions and environmental variables. The inherent subjectivity of the tests can also dispute their reliability in court.