Field Sobriety and Breath Tests—What You Need to Know

The enforcement of laws pertaining to driving under the influence of alcohol and driving under the influence of drugs (DUI and DUID, respectively) are based on a scientific urine, breath, or blood test. Field sobriety tests — administered on-site, where the officer has pulled over the motorist — include both physical or cognitive tests, as well as a preliminary breath test.

The physical tests approved by the National Highway Traffic Safety Administration (NHYTSA) are a one-leg stand, a walk-and-turn, and what is known as a horizontal gaze “nystagmus” test. The latter of these, the horizontal gaze, involves the slow movement of a pen or penlight while the police officer observes the driver’s eyes. Telltale clues in the nystagmus test are when the eyes falter in following the pen.

Cognitive tests include counting an officer’s fingers, reciting the alphabet and counting backwards.

Note that these tests face criticism and can be challenged in court. For example, the nystagmus test is criticized for giving false readings for individuals with certain medical conditions. Other medical conditions, diagnosed and not-yet-diagnosed, can complicate readings of the one-leg and walk-and-turn tests.

A Breathalyzer® test administered at a processing center or police station might be subject to dispute as well because the equipment is sometimes calibrated incorrectly.

However, by law in Pennsylvania, refusal to submit to chemical testing — Breathalyzer, blood or urine testing — can lead to a 12-month suspension of driving privileges. All drivers licensed by the state agree to this condition as part of the privilege of driving when they get a driver’s license.