Sobriety Tests and Stops Text Size:

Field sobriety tests (FSTs) are used by police officers as part of the process of identifying and arresting drivers who are suspected of driving under the influence or driving while intoxicated. These results may be used as part of the case against you if you are charged with a DUI-DWI offense. Upon being stopped by a police officer, you may be faced with a request to perform FSTs, whether you drink or not. Familiarity with the common FSTs conducted by the police, how the test results are interpreted and used, and the shortcomings of FST methods is knowledge you should have as an educated and prepared driver.

While there is a large body of research supporting the validity and accuracy of FSTs commonly used by police, there is also a lot of controversy associated with FSTs. Your defense attorney's skill and experience can be key in identifying facts and conditions about your situation in order to challenge FST results.

The Standard Field Sobriety Test Battery

There is a common standardized battery of 3 FSTs, which resulted from studies by the National Highway Traffic Safety Administration (NHTSA):

1. The one-leg stand test, in which a driver is asked to stand with arms down and one foot suspended about 6 inches above the ground
2. The walk-and-turn (WAT) test, in which a driver is asked to walk a straight line, placing the heel of the stepping foot at the toe of the back foot, turning, and walking back
3. The horizontal gaze nystagmus (HGN) test, in which a driver is asked to track a moving object with his eyes while holding his head steady

In an HGN test, the police officer will move an object, typically a penlight, across a driver's field of vision, and will watch for a characteristic jerking or bouncing movement (nystagmus) of the driver's eyes when the eyes are positioned at a far horizontal point. Nystagmus is often present when a person has a blood alcohol content of .10% or more.

NHTSA studies have shown that a combination of tests, particularly the WAT and HGN tests, can be very accurate in detecting intoxication at levels of .10% or higher, but it should be remembered that FSTs are designed to measure impairment, and do not reveal the cause of impairment.

Stopping Your Vehicle

Before you are asked to get out of your car to submit to FSTs, the police officer has already stopped your car, based on a traffic violation or the suspicious motion of your car (this might include weaving, wide turns or riding the center line of the road). You also might have been stopped at a sobriety checkpoint or roadblock, which can be a valid method for the police to keep drunk drivers off the road, or to apprehend suspects in other types of crimes. While you are still in the car, the officer will be looking for signs of intoxication based on your responses, both vocal and physical, in the course of asking you for your license and registration, or inquiring whether you have been drinking.

Your FST performance may give the police officer probable cause to arrest you for a DUI-DWI offense; a breath or blood test may follow in order to determine your blood alcohol content (BAC).

Challenging FST Evidence

Your defense attorney may seek to challenge the admissibility of FST evidence at trial in several ways, including challenging the police officer's conduct in both stopping your vehicle and the method of conducting and interpreting the FSTs, challenging the accuracy of the test results based on your situation, and the specific use of FST evidence against you in proving your level of intoxication.

The accuracy of FST methods may be negatively affected by:

• The driver's age, weight, and physical condition
• A wide variety of illnesses and medications, or the use of contact lenses
• Less-than-optimal roadside testing conditions
• The police officer's training and skill in conducting and interpreting FSTs
• Lack of baseline performance against which to judge a driver's FST results

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