Police officers typically administer a three test battery of field tests to DUI suspects. These three tests are the one leg stand, the walk and turn, and the horizontal gaze nystagmus test. The three tests are often referred to as NHTSA tests as the National Highway Traffic Administration, through the Southern California Research Foundation, standardized and developed the three tests battery. Since that time NHTSA has financed and conducted additional validation "studies" on the tests.
Officers love to testify that the tests are validated and standardized. This testimony gives the tests an aurora of scientific validity. The truth is that the tests have never been subject to to real scientific peer review. These validation studies smack of bias as they designed and conducted by the very same parties interested in using the tests for DUI enforcement.
The underlying concept of the field tests is that they test divided attention, which is necessary in driving. For instance, when you drive, you must divide your attention between several tasks, such as steering, breathing, navigating and signaling. The theory is that alcohol impairs a driver's ability to multi-task or divide attention.
At trial, Officers routinely are permitted by judges to take the stand and testify as experts on alcohol intoxication. The officers testify that alcohol impairs a person's ability to divide attention or multi-task. They then detail a DUI suspect's poor performance on these "tests." The offices, under the careful questioning of prosecutors, provide little or no information regarding the limitations of the tests. Jurors are left with the insinuation that the only real cause of poor performance on these tests is alcohol intoxication.
Of course, this absolutely not true. What the officers will never volunteer, and don't want the jury to know is that many people perform poorly on these tests when they are not under the influence of alcohol or any other mind altering substance. The fact is, not everybody has either the physical ability or the divided attention skills to perform the tests.
The tests begin with the assumption that the test subject has the physical ability to adequately perform the tests when sober. This is an assumption that cannot be validated and is not always true. Some people are more coordinated then others. Some people can do them, and some can not, even if their lives depended upon it. Because the tests do not take into consideration a person actual ability to perform the tests sober, there is no accurate way to judge whether a person is actually impaired in some way.
Furthermore, if the test subject is "impaired" in some way, the tests also have no ability to actually determine what is impairing the person. While alcohol could be the cause of impairment, impairment may also be caused any number of things such as fatigue or anxiety.
The Tests Are Voluntary
Field sobriety tests are can be considered mandatory, but at the same time, you can't be forced to do them. If you refuse to do them the police will deprived of evidnce whcih they are seeking to use gainst you. Do not assume that because you are sober you will pass them. Remember, the person grading them is biased. The officer conducting the tests most likely has already assumed you are impaired and is building a case against you. While they often portray themselves as just "seeing if you are OK to drive" they are not neutral. They would not be asking you to do the tests unless they already believed your ability to drive was likely impaired by alcohol or drugs.