Most people joke about not being able to walk a straight line when they are sober, let alone after drinking. Even though you might even say this in jest, the sentiment makes a valid point. Not everyone can walk a straight line, and that fact could result in an arrest on suspicion of DUI.
Why do police use field sobriety tests?
The simple answer is that field sobriety tests used to be the only way to determine probable cause to arrest someone for driving under the influence since portable breath testing machines did not come until much later.
Prior to the late 1970's, officers used a variety of tests. Then, the Southern California Research Institute (SCRI) evaluated several of the testing methods in order to determine which ones were most effective at the behest of the National Highway Traffic Safety Administration (NHTSA).
The SCRI determined that the following three tests yielded the most reliable results:
- Walk and turn
- One-leg stand
- Horizontal gaze nystagmus
Unfortunately, the error rate was approximately 47 percent. In order to reduce that percentage, the administration of these tests was standardized, which appeared to improve their accuracy as follows:
- Walk and turn -- 68 percent
- One-leg stand -- 65 percent
- Horizontal gaze nystagmus -- 77 percent
If officers used all three tests, accuracy peaked at 82 percent, which the SCRI and NHTSA found acceptable.
The science does not support the use of these tests based on those percentages
The hallmark of DUI arrests remains field sobriety tests even though they are inherently flawed. Scientists argue that even though they might indicate blood alcohol content level a portion of the time, they do not necessarily prove that a driver is unable to operate a vehicle.
Too many factors can cause an individual to fail one or all of these tests. An individual's physiology influences whether these tests accurately predict intoxication. The officer might not administer the tests correctly due to poor training or some other factor.
So what does all of this mean for my DUI case?
Your attorney should challenge the results of the field sobriety tests given to you, especially if the officer based your arrest on them. Even a first DUI affects nearly every aspect of your life, and you have the right to question all of the alleged evidence. If the evidence does not stand up in court, the outcome could be an acquittal or dismissal of the charges.