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Boise Dui Lawyer Explains: The Basics of Standardized Field Sobriety Tests

Background and Development of Standardized Field Sobriety Tests

Field Sobriety Tests (FSTs) are mechanisms law enforcement officers utilize to identify drivers under the influence of alcohol or drugs and they are an important part of the investigation that a good DUI lawyer will investigate. The need for a standardized system resulted in the National Highway Traffic Safety Administration (NHTSA), in collaboration with the Southern California Research Institute, embarking on a series of research studies in the 1970s. These aimed to develop consistent methods of testing driver impairment, resulting in the Standardized Field Sobriety Test (SFST) battery.


The standardized field sobriety tests comprise three primary tests that your Boise DUI lawyer will want to review closely: the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn (WAT), and the One-Leg-Stand (OLS). When properly administered, these tests provide an effective and reliable method for establishing probable cause for DUI arrests.


Standardized Field Sobriety Tests and Their Scoring System

  1. Horizontal Gaze Nystagmus (HGN): This test checks for involuntary jerking of the eye as it gazes to the side, a phenomenon often exacerbated by alcohol. Officers score the HGN test on three indicators of impairment per eye: lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees. Four or more cues suggest a blood alcohol concentration (BAC) of 0.08 or more.

  2. Walk-and-Turn (WAT): This 'divided attention' test measures a person's ability to perform physical movements while following instructions. The test involves nine heel-to-toe steps along a straight line, a turn on one foot, and nine heel-to-toe steps back. Two or more indicators of impairment suggest a BAC of 0.08 or higher.

  3. One-Leg-Stand (OLS): Another divided attention test, the subject stands on one foot while counting aloud until instructed to stop. Two or more indicators of impairment suggest a BAC of 0.08 or higher.

According to NHTSA research, when these three tests are combined, they have an accuracy rate of 80-90% for detecting alcohol-induced impairment.


Challenges with SFSTs for Drug Impairment

While SFSTs may provide a reliable tool for alcohol impairment, they present some limitations when applied to impairment caused by medications or drugs. These substances can cause symptoms such as dizziness, lethargy, blurred vision, poor coordination, and slowed reaction times, affecting an individual's cognitive and motor functions similarly to alcohol.


However, the scoring system used for alcohol impairment may not align perfectly with drug impairment. For instance, certain medications might cause visible physical or cognitive impairment but not lead to clear signs of impairment on the HGN test. In contrast, some drugs, particularly central nervous system depressants and specific types of prescription medication, can lead to symptoms similar to alcohol intoxication. Therefore, these substances might result in a 'failed' HGN test similar to alcohol impairment.


Role of Drug Evaluation and Classification Program (DECP)

Recognizing the limitations of SFSTs for detecting drug impairment, the NHTSA developed the Drug Evaluation and Classification Program (DECP). This includes a 12-step process, administered by a specially trained Drug Recognition Expert (DRE), to identify drug impairment and classify the type of drug causing the impairment.


However, SFSTs play a critical role in this process. It's often the initial SFSTs that lead an officer to suspect drug impairment and bring in a DRE for a more detailed examination. The SFSTs serve as the preliminary screening method, allowing officers to identify potential impairment before pursuing more specific and comprehensive drug detection methods.


Considerations for Legal Defense

Standardized field sobriety tests remain an essential piece of evidence for DUI prosecutions, but as any good DUI lawyer will tell you, the interpretations is subjective and can be influenced by factors such as the officer's training, environmental conditions, and the individual's physical or medical conditions. It's also important to understand that the correlation between performance on SFSTs and impairment, especially for drugs other than alcohol, is not exact.


In instances where SFSTs are the primary evidence of alleged impairment, effective DUI defense strategies may include challenging the administration and interpretation of the tests, the officer's training, or the physical or medical conditions of the defendant that might have affected test performance. While SFSTs are tools for identifying impaired drivers, they are part of a larger process that includes observation of driving behavior, physical signs and symptoms of impairment, and the results of chemical tests.


Although SFSTs are widely used and accepted as indicators of impairment, they are not infallible, and their effectiveness can be influenced by a variety of factors. A good DUI defense attorney considers the following potential shortcomings and how they might affect the reliability of the SFST results:


1. Administration and Interpretation of the Test

One of the most common areas of challenge lies in the administration and interpretation of the SFST. Officers are trained to administer these tests in a standardized manner, but human error or deviations from the standard procedure can occur. Small mistakes or misunderstandings can significantly impact the outcome of the test. For example, the officer may have inadequately explained the instructions or misinterpreted the test results.


2. Officer Training and Experience

The level of the officer's training and experience can also come into play. Officers need specialized training to administer and interpret SFSTs correctly, and even with training, there may be inconsistencies in application. If an officer has not been adequately trained or lacks experience in administering these tests, the reliability of the results can be questioned.


3. Physical or Medical Conditions

Another potential shortcoming is the subject's physical or medical condition. Factors such as age, weight, physical disabilities, or medical conditions (like neurological disorders) can affect the subject's ability to perform these tests, even when sober. Certain medical conditions can also mimic signs of intoxication, such as certain eye disorders that can lead to nystagmus, which can be misinterpreted in the HGN test.


4. Environmental Conditions

The environmental conditions under which the tests were administered can also influence their reliability. Poor lighting, bad weather, uneven or slippery surfaces, or even heavy traffic passing by can make it more challenging for a sober person to successfully complete the tests.


5. Psychological Factors

Psychological factors such as stress, anxiety, or nervousness can also impact the performance on these tests. An individual, when pulled over by a police officer and asked to perform these tests, might feel nervous or stressed, which can impact their ability to perform well on the tests.


6. Limitations with Drug Impairment Detection

As discussed earlier, SFSTs have limitations when it comes to detecting impairment caused by substances other than alcohol. While they can often detect signs of impairment, they don't provide a foolproof method of identifying the specific substance causing the impairment.


7. Absence of a Control for Individual Performance

The SFSTs do not account for a person's sober "baseline" performance. As a result, people who are naturally clumsy or uncoordinated may seem impaired when they are not. Without a control for individual differences, it can be challenging to determine whether observed "clues" are due to impairment or merely individual quirks.


Consequences of Failing SFSTs

A driver’s failure SFSTs generally gives the officer probable cause to make an arrest for DUI. In some jurisdictions, like Idaho, failing even a single test can give the officer legal grounds to make an arrest, as long as there are other subjective signs of impairment. Likewise, refusing to do the tests may give the officer legal grounds to arrest, under the idea that refusing to cooperate is evidence of a “guilty mind.”


Once the officer has probable cause to arrest, he will most likely ask the individual to submit to an evidentiary test for alcohol or drugs. The evidentiary test is the most important piece of evidence that the officer wants to obtain and that is what all of the field sobriety tests have been leading up to. Refusing the evidentiary test can result in some tough consequences. Even if you are factually innocent of a DUI, refusing an evidentiary test in Idaho can result in the loss of one’s driver’s license for a full year, with no option for restricted privileges (to drive to work, medical appointments, etc.).


If you need help with a DUI in Idaho, call Boise DUI Lawyer Cody Long at (208) 287-3303.

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