However, even under optimal conditions and clear instructions from the officer, the FSTs are not conclusive proof of impairment. Although the FSTs can serve as one piece of a much more complex DUI puzzle, the burden on the state to prove each of the elements of DUI beyond a reasonable doubt require far more then an officer’s observations of the FSTs.

Can Prior Injuries or Diagnosis Explain FST Failure?

In some cases, the lack of balance, which plays a significant role in all 3 of the FSTs, can be explained due to medical conditions that impact a defendant’s ability to maintain a balanced position, especially under the stressful circumstance of a DUI investigation.

Have you suffered a lower body injury? Have you suffered a concussion or other brain injury. Do you have high sensitivity to light or occasions of Vertigo? If so, it is important to gather records of these injuries through your medical providers in order to provide some context as to the failure of the FSTs.

Did a Car Accident Occur Prior to FSTs?

In some cases, a defendant is requested to perform FSTs shortly after they were involved in a motor vehicle accident. Although there is no hard and fast rules prohibiting FSTs from being taken after an accident has occurred, the injuries sustained as a result of the crash can cast into doubt the validity of the tests.

Even in situations where the defendant is not transported to the hospital, it is still important to be evaluated by a medical professional in order to determine the extent of the bodily damage that was sustained. If a defendant declines all treatment, this important evidence as to their condition at the time of performing FSTs is lost, making it harder to explain to a judge or jury the impact this accident had on balance and the comprehension of officer instructions.

Age and Weight Can Raise Doubt as to FST Performance

Although not considered definitive, the National Highway Safety Association has found that individuals over the age of 65 and those who are 50 or more pounds overweight may have a more difficult time performing the FSTs even if not under the influence. Officers are encourage to take these factors into consideration when determining probable cause for a DUI arrest.

Even if the defendant is still arrested, using the NHTSA recommendations can cast doubt as to the validity of the FSTs, especially in cases where additional medical conditions are also a concern.

Gather Your Medical Records Early in a DUI Prosecution to Determine Whether a Defense Exists to the FSTs

It is not illegal to be off balance. Explaining the underlying cause of imbalance through medical testimony can be an impactful way to argue to a jury that the results of the FSTs in a Vermont DUI prosecution should be significantly discounted, or, in some cases, all together ignored. By putting together a medical chronology that supports a medical defense to a DUI, a defendant may be able to show that alcohol or drugs were not the underlying factor of their roadside behavior.

The information contained in this post is for informational purposes only. Any reader who has specific questions about the DUI or any other legal process should consult with their own private attorney.

“The training I received is vital to my practice of Vermont DUI defense” stated Chadwick.  “By receiving the exact training law enforcement officers receive I am now able to better understand the nuances of the application of the field sobriety tests that may cause their application on the roadside to be questioned.”

Attorney Chadwick anticipates furthering his education in the near future, as he has been invited to attend the field sobriety instructor training this winter, which will allow him to apply for field instructor certification.  “Educating myself on the many facets of Vermont DUI defense has always been my long term goal” stated Chadwick.  “The more I understand the DUI investigation and where mistakes can be made, the better I can serve my clients in ensuring they receive the best defense possible”.

Defined as the “involuntary jerking of the eyes that occurs when eyes gaze to the side” the HGN has been validated as one of the most reliable indicators of driver impairment when compared with all the other field sobriety and investigative tests officers employ while on the roadside.

If HGN is conducted correctly a 2013 San Diego validation study has found that it can be 88% accurate in detecting that a motorists BAC is above .08. The findings in an HGN test alone can give an officer the probable cause they need to arrest a motorist and bring them back to the barracks where an evidentiary breath test is taken.

As is the case with all field sobriety tests however, the key determination in the HGN is if the test was in fact administered properly according to National Highway Safety Administration (NHTSA) standards.

As a certified HGN practitioner who has gone through the certification process of administering the HGN, I can say with conviction that the NHTSA requirements are difficult to administer correctly in a controlled classroom environment, let alone in the wide variety of environmental conditions that an officer would face when conducting an HGN test on the roadside.

Timing, position of the stimulus (object motorist is to follow with eyes), medical conditions (such as head injuries) and the surrounding environment are but a few of the many factors that can play a role in the accuracy of the HGN. If any of these are comprised by failing to follow NHTSA guidelines, the entire test and, in turn a significant portion of the DUI investigation can be compromised, leaving serious doubt as to whether the officer has the evidence necessary to charge a motorist with DUI.