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What are the components of a standardized field sobriety test?

On Behalf of | May 30, 2024 | Firm News

A police officer who pulls someone over due to suspicion of drunk driving needs to determine what’s going on with the driver so they know how to proceed. Making this determination often starts with talking to the driver. From there, the officer may take other steps to determine if the driver is impaired.

One option police officers have is the standardized field sobriety test (SFST). This is a battery of three specific tests that’s endorsed by the National Highway Traffic Safety Administration. As long as these tests are performed precisely, they’re considered accurate enough to be admissible in court.

Horizontal gaze nystagmus

The horizontal gaze nystagmus (HGN) test checks for involuntary jerking movements of the eyes, which are often exaggerated when a person is under the influence of alcohol. During this test, the officer instructs the driver to follow an object, such as a pen or a small flashlight, with their eyes.

The officer observes the eyes for three specific indicators of impairment: lack of smooth pursuit, distinct nystagmus at maximum deviation and onset of nystagmus before reaching a 45-degree angle. If the officer detects four or more out of six possible clues (three in each eye), the driver is likely impaired.


The walk-and-turn test assesses a person’s ability to perform tasks requiring divided attention. The driver is instructed to take nine heel-to-toe steps along a straight line, turn on one foot and return to the starting point in the same manner.

The officer looks for eight specific clues of impairment: inability to balance during instructions, starting before instructions are finished, stopping while walking, failing to touch heel-to-toe, stepping off the line, using arms to balance, making an improper turn and taking an incorrect number of steps. If the driver exhibits two or more of these clues, it indicates a high likelihood of impairment.

One-leg stand

The one-leg stand test also evaluates balance and coordination. The driver is asked to stand with one foot approximately six inches off the ground and count out loud starting from one thousand, continuing until told to stop, typically for 30 seconds.

During this time, the officer observes for four clues of impairment: swaying while balancing, using arms to balance, hopping to maintain balance and putting the foot down before instructed. Exhibiting two or more of these clues suggests impairment. This test requires concentration and physical stability, both of which are adversely affected by alcohol consumption.

If one or more SFST test components indicates impairment, the driver may be asked to take a chemical test to determine their blood alcohol concentration. They may be arrested for drunk driving, which triggers the need for a defense strategy. Working with a legal representative who can assist with a defense strategy is critical for any defendant who wants to determine the viable options for fighting the state’s case against them.