What are the Standardized Field Sobriety Tests (SFST’s) used in a
These are roadside tests used by law enforcement officers to assist them
in determining if there is probable cause to arrest a person for driving
under the influence (DUI). These tests have been validated by numerous studies sponsored by the
National Highway Traffic Safety Administration (NHTSA). These
field sobriety test validation studies will be covered in more detail in a later article.
There are (3) standardized elements to the SFST’s:
Standardized Administrative Procedures
- All officers must administer the SFST’s the same way every time.
- All officers must look for the same clues on each test.
- All officers must use the same criteria to determine if a clue is present.
The (3) field sobriety tests are:
- Horizontal Gaze Nystagmus (HGN)
- Walk and Turn
- One Leg Stand
Horizontal Gaze Nystagmus is the involuntary jerking of the eyes as they
look to the side. It is caused by alcohol, and certain other
drugs. The HGN test has been scientifically validated as an indicator for alcohol
influence, and judges and courts will therefore give more weight and credibility
to the HGN test than the Walk and Turn and One Leg Stand tests.
There are (3) clues officers are trained to look for in HGN:
- Lack of Smooth Pursuit
- Distinct and Sustained Nystagmus at Maximum Deviation
- Onset of Nystagmus Prior to 45 Degrees.
The clues are checked for in both eyes of the subject, meaning a total
of (6) clues are possible to see during the HGN. Based on validation studies
and research officers are trained on, if an officer observes 4 or more
clues, it indicates that the person’s
blood alcohol concentration (BAC) is 0.08 grams or higher. Research studies cited by law enforcement
state that this test is 88% reliable.
The Walk and Turn test is a divided attention test, meaning that the test
“divides” a person’s attention between mental and physical
tasks. This is significant because safe driving demands the ability to
divide attention between multiple mental and physical tasks. Imagine how
everyday driving divides your attention: maintaining your lane while being
aware of other vehicles' position, maintaining proper speed, safely
making movements, proper signaling, etc.
There are 2 phases and 8 standardized clues for the Walk and Turn test:
- Unable to keep balance while listening to instructions
- Starts too soon
- Steps off line
- Misses heel to toe
- Incorrect number of steps
- Improper turn
- Raises arms for balance
- Stops to balance self
Based on research cited by law enforcement, if an officer observes 2 or
more clues it indicates that the person’s blood alcohol concentration
(BAC) is 0.08 grams or more. The validation studies state that this test
is 79% reliable.
The One Leg Stand test is the second divided attention test used as part
of the 3 test battery. There are 2 phases and 4 clues for the One Leg Stand:
- Puts foot down
- Raises arms for balance
Based on the research if an officer observes 2 or more clues it indicates
that the person’s blood alcohol concentration (BAC) is 0.08 grams
or more. The research states that this test is 83% reliable.
When the tests are combined, the validation studies cited by law enforcement
state that they are 91% reliable. These tests can, of course, provide
strong evidence and assist the prosecution with convicting a person accused
of DUI when done properly.
In the next article, the administrative procedures and issues that can
arise with HGN will be covered.
About the author: Joshua Ott was a police officer for more than 10 years
in Roswell, Georgia. He has extensive experience dealing with impaired
drivers. He was a Drug Recognition Expert Instructor and is a Standardized
Field Sobriety Testing Instructor and has trained numerous officers over
the course of his career. He now operates Caselock, Inc, which provides
expert testimony and case reviews for cases involving alcohol and drug