Standard Field Sobriety Tests (SFST) are typically given when an police officer has reasonable articulable suspicion that a driver has violated Minnesota DWI law.  The failure of one or more of  the SFSTs can be  used by an police officer to establish probable cause to make a valid DWI arrest.

So what exactly are the Standard Field Sobriety Tests?  The SFSTs were developed by the National Highway Traffic Safety Administration (NHTSA) based upon research conducted by the Southern California Research Institute, and are used to establish probable cause that a person has violated DWI law, specifically, that their blood alcohol level is above the legal limit (.08 in Minnesota).

The Three Standard Field Sobriety Tests

Horizontal Gaze Nystagmus Test (HGN)

A person’s eyes naturally and  involuntary jerk as they gaze to the side.  When a person is intoxicated this jerking is exaggerated and they will have difficulty smoothly tracking a moving object.

An officer will administer the HGN test by having  a suspect follow a moving object (e.g. a pen or small flashlight) horizontally and observing three indicators of impairment in each eye: (1) if the eye cannot follow the moving object smoothly; (2) if jerking is distinct when the eye is at maximum deviation; and if the angle of onset of jerking is withing 45 degrees of center.

If the officer observes four or more clues between the two eyes (according to NHTSA research) the suspect likely has a BAC of 0.08 or greater.

The HGN test can also indicate the presence of other depressants (e.g. seizure medications, barbiturates.)

Walk-and-Turn Test (WAT)

The walk-and-turn test is termed a “divided attention” test and tests a suspect’s ability to listen to and follow instructions while performing simple physical movements.

Unimpaired individuals (in general) easily perform the WAT test while impaired individuals typically have difficulty dividing their attention between following simple instructions (i.e. a simple mental task) while also performing a simple physical task.

To conduct a WAT test the officer asks a suspect to take nine steps, heel-to-toe, along a straight line, and after taking the nine steps, to turn on one foot and return the same way.

The officer looks for eight indicators of impairment while observing the suspect, including whether or not the suspect: (1)  can keep their balance while listening to the instructions; (2)  begins before the instructions are finished; (3)  stops while walking to regain balance; (4) does not touch heel-to-toe; (5) steps off the line; (6) uses arms to balance; (7) makes an improper turn; (8) takes an incorrect number of steps.

NHTSA research indicates that the majority of individuals that exhibit two or more indicators while performing the test will have a BAC of 0.08 or higher.

One-Leg Stand Test (OLS)

The one-leg-stand test is effectively a balancing test where the officer asks a suspect to stand with one foot approximately six inches off the ground and count aloud by thousands until instructed to put their foot down.  This test is timed by the officer for 30 seconds.

During the test the officer looks for four indicators of impairment, including: (1) swaying while balancing; (2) using arms to balance; (3) hopping to maintain balance; (4) putting the foot down.

NHTSA research indicates that the majority of individuals that exhibit two or more indicators while performing the test will have a BAC of 0.08 or more.

Results of the Three Tests Used in Combination

According to NHTSA research, when the results from the combination of the three SFSTs indicate impairment, officers are accurate in the majority (91%) of cases.

Challenging the Standard Field Sobriety Tests

The following are some significant issues that can greatly affect and can be used to challenge the reliability of SFSTs.

• Testing Conditions: Rain or snow; badly lit/dark testing location;  uneven testing surface.
• Physical & Mental Disabilities of Suspect:  Current knee, hip, back injuries; corrective lenses (e.g. contacts); past knee, back, hip surgeries; cognitive disabilities; hearing disabilities.
• Improper Administration of Tests:  The officer’s improper administration of the test (e.g.  providing the instructions, recording the results) can greatly affect the reliability of the SFSTs.

Resources & References

• National Highway Traffic Administration (Main Website)
• National Highway Traffic Administration – Impaired Driving Section

Legal Disclaimer

The following is for informational purposes only and does not constitute legal advice.  Although the following information is deemed accurate and current, statutory and case law change frequently and the following information should not be relied upon as authoritative.