Field Sobriety Test
Standardized
Field Sobriety Testing
The Standardized
Field Sobriety Test (SFST) is a battery of
three tests administered and evaluated in
a standardized manner to obtain validated
indicators of impairment and establish probable
cause for arrest. These tests were developed
as a result of research sponsored by the
National Highway Traffic Safety Administration
(NHTSA) and conducted by the Southern California
Research Institute. A formal program of training
was developed and is available through NHTSA
to help police officers become more skillful
at detecting DWI suspects, describing the
behavior of these suspects, and presenting
effective testimony in court. Formal administration
and accreditation of the program is provided
through IACP.
The three
tests of the SFST are:
1. the horizontal gaze nystagmus (HGN)
2. the walk-and-turn
3. the one-leg stand.
These tests are administered systematically and are evaluated according to
measured responses of the suspect.
HGN Testing
Horizontal
gaze nystagmus is an involuntary jerking
of the eyeball which occurs naturally as
the eyes gaze to the side. Under normal circumstances,
nystagmus occurs when the eyes are rotated
at high peripheral angles. However, when
a person is impaired by alcohol, nystagmus
is exaggerated and may occur at lesser angles.
An alcohol-impaired person will also often
have difficulty smoothly tracking a moving
object. In the HGN test, the officer observes
the eyes of a suspect as the suspect follows
a slowly moving object such as a pen or small
flashlight, horizontally with his eyes. The
examiner looks for three indicators of impairment
in each eye: if the eye cannot follow a moving
object smoothly, if jerking is distinct when
the eye is at maximum deviation, and if the
angle of onset of jerking is within 45 degrees
of center. If, between the two eyes, four
or more clues appear, the suspect likely
has a BAC of 0.10 or greater. NHTSA research
indicates that this test allows proper classification
of approximately 77 percent of suspects.
HGN may also indicate consumption of seizure
medications, phencyclidine, a variety of
inhalants, barbiturates, and other depressants.
Divided Attention
Testing
The walk-and-turn
test and one-leg stand test are "divided
attention" tests that are easily performed
by most sober people. They require a suspect
to listen to and follow instructions while
performing simple physical movements. Impaired
persons have difficulty with tasks requiring
their attention to be divided between simple
mental and physical exercises. In the walk-and-turn
test, the subject is directed to take nine
steps, heel-to-toe, along a straight line.
After taking the steps, the suspect must
turn on one foot and return in the same manner
in the opposite direction. The examiner looks
for seven indicators of impairment: if the
suspect cannot keep balance while listening
to the instructions, begins before the instructions
are finished, stops while walking to regain
balance, does not touch heel-to-toe, uses
arms to balance, loses balance while turning,
or takes an incorrect number of steps. NHTSA
research indicates that 68 percent of individuals
who exhibit two or more indicators in the
performance of the test will have a BAC of
0.10 or greater. In the one-leg stand test,
the suspect is instructed to stand with one
foot approximately six inches off the ground
and count aloud by thousands (One thousand-one,
one thousand-two, etc.) until told to put
the foot down. The officer times the subject
for a 30 seconds. The officer looks for four
indicators of impairment, including swaying
while balancing, using arms to balance, hopping
to maintain balance, and putting the foot
down. NHTSA research indicates that 65 percent
of individuals who exhibit two or more such
indicators in the performance of the test
will have a BAC of 0.10 of greater. The effectiveness
of SFST in court testimony and evidence depends
upon the cumulative total of impairment indicators
provided by the three-test battery. The greater
the number of indicators, the more convincing
the testimony. Because SFST is administered
according to national standards and is supported
by significant research, it has greater credibility
than mere subjective testimony.
Alternative
Testing Methods
Sometimes,
an officer will encounter a disabled driver
who cannot perform the SFST. In such cases,
some other battery of tests such as counting
aloud, reciting the alphabet, or finger
dexterity tests may be administered. If
the proper motions are filed, these test
are usually not admissible at trial.