Research sponsored by the National Highway Traffic Safety Administration (NHTSA) indicates that when a person fails the HGN there is a 77% reliability factor in predicting a 0.10% BAC or higher. That means that 23 out of 100 people that fail the test might not be guilty.
Problems with the HGN Test
Nystagmus is defined as an involuntary jerking of the eyes. There are many causes of nystagmus that are not alcohol related. A portion of the population has naturally occurring nystagmus which will register as a positive result. An officer not administering the test properly can cause nystagmus to occur when the eye is stressed at the extremes or when the officer uses a jerky and not smooth movement when moving the pointer from side to side. Flashing lights like those from passing cars or the police vehicles can also cause nystagmus. There are also many conditions and substances that can cause nystagmus including fatigue and diseases like cataracts, hypertension, inner ear problems, and substances like antihistamines, depressants, aspirin, streptomycin, nicotine, and caffeine.
The DUI Officer Has No Baseline of Performance On The Field Sobriety Tests
The DUI officer will claim you “performed poorly” on the field sobriety tests therefore you were impaired. But “poorly” compared to what? This claim is meaningless without knowing how you would perform normally even with nothing to drink. People vary tremendously in their natural ability (or inability) to perform field sobriety tests. How well a given person performs the field sobriety tests depends on many factors: natural level of coordination and equilibrium, natural level of balance, fitness level, composure in the face of pressure, injuries, age and practice, among others.
The Standardized Field Sobriety Tests Were Not Properly Administered
The National Highway Traffic Safety Administration (NHTSA) devised national standards for how DUI officers are to administer the three standardized field sobriety tests: The Horizontal Gaze Nystagmus Test, the Walk-and-Turn Test and the One-Leg Stand Test. DUI officers often fail to adhere to these national guidelines. This opens up their whole DUI investigation to attack. Often times a DUI officer will say in his report the DUI suspect “failed” or “performed poorly” on the field sobriety tests; but when the performance is judged according to NHTSA’s national standards, the person did everything correctly! If the officer does not administer the test according to the scientific procedures of the test, the test results (your performance) has no reliability or meaning when it comes to the issue of impairment.
Non-Laboratory real world testing conditions
Standing on the side of the road, on unlevel ground, alone in the middle of the night, often times cold, with only a flashlight for light, and cars speeding by, are the conditions most people find themselves when performing field sobriety tests. Each one of these factors can affect performance on a field sobriety test which means any trouble doing the test may be because of the real world conditions and not impairment.
The Non-Standardized Field Sobriety Tests Lack Reliability
Often times officers don’t give the standardized test like they are supposed to and instead give non-standardized tests instead. The non-standardized field sobriety tests include the finger-to-nose test, the finger count test, the hand pat test, the coin pickup, the alphabet test, the reverse counting test and the Rhomberg test (tilting your head back and estimating 30 seconds). The National Highway Traffic Safety Administration (NHTSA) has set no standards for how to administer, score or interpret these tests, and no studies have ever shown them to be reliable indicators of DUI impairment.
Field Sobriety Tests Don’t measure driving Impairment
Driving a motor vehicle is a very complex activity that involves a wide variety of task and operator capabilities. It is unlikely that complex human performance, such as required to safely drive an automobile, can be measured at roadside. The constraints imposed by roadside testing conditions were recognized by the developers of NHTSA’s SFST battery. As a consequence, they pursued the development of tests that would provide statistically valid and reliable indications of a driver’s BAC, rather than indications of driving impairment. The link between BAC and driving impairment is a separate issue, involving entirely different research methods. Thus, SFST results help officers to make an accurate DUI arrest decision even though SFST’s do not directly measure driving impairment. (Final Report, Validation of the SFST Battery at ACs Below 0.10 percent.)