What You Need To Know About Field Sobriety Tests

The goal of this article is to level the playing field between law enforcement officers and drivers who are asked to perform Field Sobriety Tests (FST’s).

When an individual is stopped by a Maine law enforcement officer on suspicion of operating under the influence, they may ultimately be asked to submit to a Breathalyzer test. However, before the driver and officer reach the point of the Breathalyzer, it’s likely that the officer will ask the driver to perform Standardized Field Sobriety Tests (SFST’s or FST’s) to determine whether or not they have a reason, also known as probable cause, to make a formal arrest.

It’s important to note that the driver is not required to submit to the Field Sobriety Tests at the request of the officer.  Because the tests are used to decide whether or not to arrest the driver for OUI, it may be wise in some circumstances to respectfully decline.  If the driver declines the Field Sobriety Tests, they can still be arrested, and the fact that they declined to perform the FST’s at the request of the officer may be used at trial to prove that they were intoxicated.

If you choose to perform the Field Sobriety Tests, it’s helpful to have an idea what to expect.  As you would imagine, the officer that is administering the tests has been thoroughly trained, and is very familiar with the tests.  This places the driver at a significant disadvantage because they are likely unfamiliar with the tests being administered, are feeling nervous or scared in an unfamiliar environment, with the blue lights of the police car flashing.

There are three Standardized Field Sobriety Tests: (1) The Horizontal Gaze Nystagmus; (2) The Walk and Turn; and (3) The One Leg Stand. All three tests are “divided attention tests” which are designed to test the driver’s ability to listen to instruction as well as his or her ability to perform the tests correctly.  As the name suggests, the three tests are standardized, and should be administered and judged the same in every case.

1.  Horizontal Gaze Nystagmus (HGN)

HGN is the involuntary jerking of the eyes as they gaze towards the side. Allegedly, this is the most accurate of the three Standardized Field Sobriety Tests at detecting impairment.

In administering the test, the officer will ask if there are any medical reasons why the driver would be unable to perform this test. The officer will check the driver for equal pupil size, resting nystagmus, and equal tracking in both eyes.  If the driver’s pupils are substantially unequal size, or if the two eyes don’t track together, it may be an indicator of something other than impairment, such as a medical condition.

The officer will instruct the driver to put their feet together and have their hands at their side, keep their head still, follow the stimulus with only their eyes, and keep looking at the stimulus until the test is over. It is important to pay attention to the instructions!

During the HGN test the officer will be looking for three clues in each eye:  (1) lack of smooth pursuit; (2) distinct and sustained nystagmus at maximum deviation; and (3) onset of nystagmus prior to 45 degrees.

The HGN test consists of the officer moving a stimulus (likely a pen) side to side 15 inches from the driver’s face.  While the officer moves the pen, they will be looking for the clues mentioned above.

2.  Walk and Turn

Pay attention to the instructions! This test is just as much a mental test as it is a physical test. There is an instruction phase and a walking phase. Half of the clues the officer is looking for have to do with following the instructions.

The Walk and Turn has 8 possible clues that the officer is looking for: (1) cannot keep balance while listening to instructions; (2) starting the test to soon; (3) stopping during the test; (4) not touching heel-to-toe while walking; (5) stepping off the line while walking; (6) using arms to balance; (7) not turning correctly after the 9 steps; and (8) taking an incorrect number of steps.

The officer will ask the driver to stand with their feet heel-to-toe, with their hands to their side, while they listen to the instructions.  The driver will then be instructed to take 9 heel-to-toe steps on a straight line, then turn as instructed, and take 9 heel-to-toe steps back (while counting the steps out loud).

The Walk and Turn should be performed on a dry, hard, level, non-slippery surface with sufficient room for the driver to complete the required steps.

3.  One Leg Stand

Just like the Walk and Turn test, there are two parts: an instructional phase and a balance phase.

To start the test, the driver will be required to stand with their feet together, with their arms at their side, and listen to the instructions. The driver will then be asked to raise one foot approximately 6 inches, and count out loud to 30.

The One Leg Stand has 4 clues that the officer will be looking for: (1) swaying while balancing; (2) using arms to balance; (3) hopping; and (4) putting foot down.


All three of the Standardized Field Sobriety Tests can be difficult, regardless of whether the driver is impaired.  What officers fail to realize is that these tests are likely being performed for the first time, by a driver who is often nervous or scared, while on the side of the road.

This article was intended to provide a brief summary of the Standardized Field Sobriety Tests, and only scratches the surface of the available information. There are also additional tests that an officer may ask a driver to perform while on the roadside (such as counting backwards or reciting the alphabet).  The most important thing to do is pay close attention to the instructions.   Hopefully this article has helped prepare future drivers for what to expect if an officer asks them to complete the Field Sobriety Tests.  If you’ve been charged with a criminal driving offense in Southern Maine, contact Attorney Eric S. Thistle at the law offices of Fairfield & Associates, P.A.

Attorney Eric S. Thistle can be reached by email at eric@fairfieldandassociates.com or by telephone at (207) 985-9465.

Disclaimer: This article is intended to provide general information about Maine law. The publication of this article does not constitute an attorney-client relationship between the author and the reader.