Washington DC Field Sobriety Tests

To develop clues of impairment against someone suspected of a traffic alcohol offense, officers will likely initiate a combination of National Highway Traffic Safety Administration Standardized Field Sobriety Tests. These tests include the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn, and the One-Leg Stand. The tests are used together to provide subjective evidence of your impairment.

Horizontal Gaze Nystagmus (HGN):

The HGN test measures the natural involuntary jerking of the eye that is intensified while under the influence of alcohol or certain drugs. When impaired by the influence of alcohol, studies show there are six indicators of impairment during this test, three in each eye. The officer must find four or more of the following to conclude that the suspect is impaired:

• Subject’s eyes cannot smoothly track the pen.
• Subject demonstrates a distinct and sustained nystagmus at maximum deviation, or approximately 60 degrees from the center.
• Subject’s nystagmus begins before the eyes turn 45 degrees from the center.

Walk-and-Turn:

The subject must take nine steps along a straight line, real or imaginary, walking heel-to-toe. After taking the steps, the subject must turn in a prescribed way and return in the same manner in the opposite direction. There are eight indicators of impairment during this test, of which the officer must find two or more to conclude that the subject is impaired:

• Subject used arms for balance.
• Subject cannot maintain balance during instructions.
• Subject turns improperly.
• Subject does not take the proper number of steps.
• Subject steps off the line.
• Subject stops to regain balance.
• Subject fails to walk heel-to-toe.
• Subject begins to walk before the instructions are completed.

One-Leg Stand:

The subject must stand on one foot with the other foot held six inches off the ground, keeping both legs straight. While holding this position, he or she must count to 30 in the “one-one thousand, two-one thousand” manner. There are four indicators of impairment during this test, of which the officer must find two or more to conclude that the suspect is impaired:

• Subject used arms to balance.
• Subject swayed to regain balance.
• Subject hopped to regain balance.
• Subject put the raised foot down early.

In a highly controlled laboratory setting, the One-Leg Stand test scored only an 83% accuracy rate, the Walk-and-Turn a 79% accuracy rate, and the HGN an 88% accuracy rate at predicting a 0.10 BAC (the former legal limit for DWI).

There are many ways to question the validity of SFSTs. For example, variations in the roadside setting, the adequacy pf training of the officers, and the methods of administration can all influence test results. Because of the imperfect nature of sobriety tests, law enforcement officers often use chemical testing of BAC to provide further evidence of impairment.

If the investigating police officer deems it necessary, a chemical examination through the use of blood, urine, or breath samples may be used to determine the alcohol content of a suspect.  An Intoxilyzer, also known as a Breathalyzer, is the most common means of measuring BAC.