When Harris County law enforcement officers pull over a driver on suspicion
of drunk driving, they typically administer one or more field sobriety
tests. The results can be used by the officer to establish probable cause for a
DWI arrest, and as evidence in support of a conviction at trial.
There is a standard battery of three field sobriety tests which can be
given. The first is known as the walk-and-turn. In this test, the officer
directs the suspect to walk a specified number of steps in a straight
line, heel-to-toe, and then turn on one foot and walk back along the same
straight line. The officer will note whether the suspect steps out of
line, fails to keep heels to toes, stops to maintain balance, or uses
their arms to stay balanced. Any of these is considered a sign of impairment.
The second test is known as the one-leg-stand, which is exactly what it
sounds like. The suspect is told to lift one foot off the ground while
counting, for a period of about 30 seconds. Hopping to keep balanced,
swaying or using arms for balance, or putting the foot down are considered
indicators of impairment.
The third test is the horizontal gaze nystagmus. In this test the officer
asks the suspect to follow a flashlight or pen with their eyes as the
officer moves it horizontally. An impaired person will often experience
an involuntary jerking of the eyes while doing this, and may have trouble
tracking the moving object evenly.
There are two major problems with the standard field sobriety tests. First,
they depend heavily on the subjective observations of the arresting officer.
Second, they fail to take into account other factors that can affect a
suspect's ability to perform the tests, such as age, weight and medical
condition. An experienced DWI defense attorney can often call into question
the results of field sobriety tests, casting doubt on the prosecution's case.
Source: NHTSA.gov, "Development of a Standardized Field Sobriety Test,"
accessed Oct. 25, 2014