DUI Traffic Stops: What to know (Part 3 of 3)

This is the third of our 3-part series that takes a look at the reality of being pulled over for suspicion of DUI, what rights you have in this situation and the details of each standard field sobriety tests (SFST).

In no way does RGP condone drinking and driving.

Part Three: Standardized Field Sobriety Tests

The following are descriptions and facts regarding the 3 main Standard Field Sobriety Tests (SFST).

One-Leg Stand

In the One-Leg Stand test, the suspect is instructed to stand with one foot approximately six inches off the ground and count aloud by thousands (One thousand-one, one thousand-two, etc.) until told to put the foot down. The officer times the subject for 30 seconds. The officer looks for four indicators of impairment:

  • Swaying – Using arms to balance (raising or using arms more than 6 inches)
  • Using arms to balance (raising or using arms more than 6 inches)
  • Hopping
  • Putting the foot down before 30 seconds.

If the subject exhibits two or more of the above clues, the inference is that they are impaired.

The test is 65% accurate in detecting intoxicated individuals, in and of itself, with no other tests and 83% accurate when combined with 4 or more clues from the HGN.

Walk and Turn

The Walk-and-Turn test and One-Leg Stand test are “divided attention” tests that are easily performed by most unimpaired people. They require a suspect to listen to and follow instructions while performing simple physical movements. Impaired persons have difficulty with tasks requiring their attention to be divided between simple mental and physical exercises.

In the Walk-and-Turn test, the subject is directed to take nine steps, heel-to-toe, along a straight line. After taking the steps, the suspect must turn on one foot and return in the same manner in the opposite direction. The examiner looks for eight indicators of impairment:

  • The suspect cannot keep balance while listening to the instructions
  • Begins before the instructions are finished
  • Stops while walking to regain balance
  • Does not touch heel-to-toe
  • Steps off the line
  • Uses arms to balance
  • Makes an improper turn
  • Takes an incorrect number of steps.

NHTSA research indicates that 79 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.08 or greater (Stuster and Burns, 1998).

HGN Testing

Horizontal Gaze Nystagmus is an involuntary jerking-of-the-eye that occurs naturally as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. An alcohol-impaired person will also often have difficulty smoothly tracking a moving object. In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object such as a pen or small flashlight, horizontally with his or her eyes. The examiner looks for three indicators of impairment in each eye:

  • The eye cannot follow a moving object smoothly
  • Jerking is distinct when the eye is at maximum deviation
  • The angle of onset of jerking is within 45 degrees of center

If, between the two eyes, four or more clues appear, the suspect likely has a BAC of 0.08 or greater.

NHTSA research found that this test allows proper classification of approximately 88 percent of suspects (Stuster and Burns, 1998). HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.

We hope that this series has given you some insight into the procedures, your rights and the testing of a DUI traffic stop. However, we remind you again, don’t drink and drive. But if you do, be smart about your interaction with the police. And be sure to call our office for help.


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