Drunk driving field sobriety tests explained

By James Morton

You have seen it in the movies and on television shows: Someone is pulled over, and the police officer asks him to stand on one leg and recite the alphabet.

What is the purpose of this strange-looking exercise? It is part of the Standardized Field Sobriety Test (SFST) series administered roadside to see if there is probable cause to charge someone with drunk driving. The tests are simple and require no equipment.

There basically are two common types of drunk driving field sobriety tests: HGN Testing and Divided Attention Testing. Here is a rundown of what each involves and what officers are looking for.

HGN Testing

Horizontal gaze nystagmus (HGN) is when the eyeball jerks involuntarily. This happens naturally as someone looks to the side and up. When someone is under the influence of alcohol, though, the jerking is exaggerated and may occur at lesser angles. An alcohol-impaired person also will often have trouble tracking a moving object. In the HGN test, the officer watches as the suspect follows a slowly moving object such as a pen or small flashlight horizontally with his eyes.

The examiner is looking for three things: 1) if the eyes cannot follow a moving object smoothly, 2) if the eyes jerk when moved as far to the side as possible and 3) if the jerking begins when the eyes are moved less than a 45 degrees.

This test is considered highly accurate if administered properly. Most police officers are not medical experts, though, and attorneys have successfully challenged arrests if the officer has not been trained properly.

Divided Attention Testing

Divided attention tests require a driver to follow instructions while performing simple movements. That is because impaired people have difficulty with tasks requiring their attention to be divided between mental and physical exercises.

There are a number of variations, including tests that require counting backwards, touching the nose and reciting the alphabet. There are only two tests, however, that the National Highway Traffic Administration considers standard: the walk-and-turn test and the one-leg stand test.

Walk-and-Turn Test

The driver takes nine steps, heel-to-toe, along a straight line then turns on one foot and walks heel-to-toe back in the opposite direction. The officer looks to see if the driver shows any of the seven signs of impairment:

  • cannot keep balance while listening to the instructions
  • begins before the instructions are finished
  • stops to regain balance while walking
  • does not touch heel-to-toe
  • uses arms to balance
  • loses balance while turning
  • takes an incorrect number of steps.

National Highway Traffic Safety Administration research indicates that 68 percent of the people who show two or more of these signs will have a BAC of 0.10 or greater. In South Carolina, 0.08 is the legal limit.

One-Leg Stand Test

The driver stands with one foot about six inches off the ground and counts 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 and looks for four signs of impairment:

  • swaying while balancing
  • using arms to balance
  • hopping to maintain balance
  • putting a foot down.

The Right to Refuse an FST

Every driver has the right to refuse to take a roadside sobriety test. Declining to take a roadside test does not carry the same consequences as refusing to take a Breathalyzer, though drivers can be arrested on suspicion of DUI for refusing.

If you have been charged with a DUI and have any questions about the way the arrest was handled, you should consult an attorney for advice. At Morton & Gettys, our experienced drunk driving lawyers can work with you to make sure your rights are protected. Call us today for a free consultation.

James Morton is an attorney with Morton & Gettys Law Firm in Rock Hill, SC. A former prosecutor, his practice incorporates a range of criminal cases, including DUI. You can reach him at (803) 366-3388.

Information or interaction on this page should not be construed as establishing a client-attorney relationship or as legal advice. For advice about your specific situation, please consult one of our attorneys.