Houston Criminal Defense Blog

What Is a Field Sobriety Test?

When a law enforcement officer suspects that a driver is under the influence of alcohol or drugs, the officer often asks the driver to submit to a series of voluntary evaluations. These tests, commonly referred to as field sobriety tests, are designed to evaluate the driver’s balance and other motor skills. The most common tests, known as “standardized” field sobriety, were developed by the U.S. National Highway Transportation Safety Administration (NHTSA) and were found to be the most effective at determining a driver’s level of impairment. Officers are expected to administer these tests in a very specific manner for them to be considered “valid.” The tests, in order, are as follows:

1) Horizontal Gaze Nystagmus (HGN). The HGN test is the only scientifically based test in the battery and is conducted when the officer positions a pen or other stimulus approximately 12 inches away from the driver’s face and asks him to follow it with only his eyes as the stimulus is moved from side to side. The evaluator is looking for the driver’s eyes to involuntarily jerk as the stimulus is followed.

2) Walk-&-Turn (WAT). The WAT is one of two divided attention tests which ask a driver to perform a mental task at the same time as a physical task, which is required while driving. The driver is asked to take a series of heel-to-toe steps, turn around, and take a series of steps back. There are 8 different criteria that officers look for including the driver’s ability to follow detailed directions, balance, and walking.

3) One Leg Stand (OLS). The OLS is the second divided attention test and requires a driver to stand on one foot while counting out loud. Officers watch the driver for raising his arms for balance, putting a foot down, swaying, or hopping.

There are other tests that are sometimes administered as well such as the alphabet test, finger to nose, and finger counting tests. These tests have no rules for administration and hold little to no value in court.

Very often, the only testing done in the field is a hand held “alco-sensor” which can only be referred to as being positive or negative in a courtroom setting.

All roadside tests are considered voluntary and no legal penalties will be faced if refused. However, many officers will view a refusal as an admission of guilt and will arrest the driver.

Categories: Criminal Defense, DWI