With the universal adoption of statutes that make it a crime to operate a motor vehicle at or above a certain blood alcohol content level, field sobriety tests have diminished in importance in most DUI cases. It is no longer necessary for the prosecution to prove impairment in order to obtain a conviction in the typical DUI case.
Nonetheless, field sobriety tests can play a critical role in certain DUI cases. For instance, in many states it is a crime to operate a motor vehicle with a blood alcohol content level at or above .08%, but it is also a crime to operate a vehicle while impaired even with a lower blood alcohol content (BAC) level. In those cases, the prosecution must prove that the driver was impaired, and field sobriety tests are the most commonly accepted and scientific means of proving impairment.
Field sobriety tests can also provide critical evidence against a DUI defendant when the blood or breath alcohol test results are questionable or are excluded as evidence.
Fortunately, in most states, field sobriety tests are not mandatory. That means that in most states, there is no penalty for refusing a field sobriety test and a driver cannot be compelled to take one.
For those drivers who have already participated in field sobriety testing, the results may be subject to challenge if the tests weren’t conducted properly-and field sobriety testing allows a lot of room for error and subjectivity.
Since 1981, the National Highway Transportation Safety Administration (NHTSA) has provided a standardized model for field sobriety testing. Not all states or local law enforcement agencies mandate the use of these standardized procedures, but the simple fact that the NHTSA has determined the “most reliable” approach to field sobriety testing can create a point of attack for DUI attorneys in cases where these procedures were not followed.
The NHTSA model requires the administration of three field sobriety tests: the One Leg Stand Test, the Horizontal Gaze Nystagmus (HTN) Test, and the Walk and Turn (WAT) Test. NHTSA data clearly indicates that the accuracy of field sobriety testing declines dramatically when only one or two of these tests are performed.
The model depends on the use of all three tests, and on strict procedures being followed for the administration of each test. Even when all three tests are used in conjunction and administered according to NHTSA procedures, assessments are accurate in only 91% of cases. And, of course, most field sobriety test administrations are not conducted perfectly.
Field sobriety tests are primarily intended as a tool for officers to determine whether or not further action is required, and in those cases aren’t likely to have a significant impact on the outcome of the case. However, in those cases in which field sobriety test results are critical to the prosecution, either because of a low BAC or because the BAC test wasn’t properly administered, deviation from the NHTSA guidelines may provide the weak point at which a DUI lawyer can crack the prosecution’s case.