The NHTSA established eight field sobriety tests to determine drug usage: horizontal gaze nystagmus (HGN), pupil reaction, pupil size, standing steadiness, one-leg stand, walk-the-line, finger-to-nose, and pulse rate.
Officers also consider skin marks, apathy, drowsiness, and hyperactivity. Although relatively accurate indicators of drug use, the reliability of the results is contingent upon the training and experience of the office administering tests.
NHTSA established several field sobriety tests to determine drug use. Eight tests were developed – one leg stand, finger-to-nose, walk –the-line, standing steadiness, HGN, pupil reaction, pupil size, and pulse rate. Officers also consider skin marks, apathy, drowsiness, and hyperactivity. Although the tests are considered good indicators of drug use, their reliability depends on the training and experience of the officer.
The preliminary breath test (PBT) is offered at the scene of a police stop to determine motorist intoxication. The PBT is part of the implied consent law, and in a few states refusing to take the test can result in a lengthier driver’s license suspension. Although the PBT result is not admissible in criminal proceedings, it is usually admissible in a driver’s license suspension hearing. Since the PBT is not accurate or widely accepted as reliable scientific evidence, it cannot be used to prove criminal guilt beyond a reasonable doubt; however it can be used to prove civil culpability by a preponderance of the evidence (more likely than not) is a driver’s license suspension hearing.
PBT reliability is significantly influenced by external factors unrelated to alcohol consumption. Depending upon PBT model used, the result can be skewed and inflated by non-tethanol components. The fuel cell PBT is distorted by the presence of acetaldehyde, methanol, isopropanol and n-propranolol. The gas sensor PBT has inflated results with the previously mentioned chemicals, as well as acetic acid, paraldehyde, and ethylene glycol. In most studies performed, the PBT was found to be 60-80% accurate.