Drunk Driving:

Field Sobriety and Chemical Tests

Field Sobriety Tests:

The most commonly used FSTs are:

  • Horizontal gaze nystagmus test (following an object with the eyes to determine characteristic eye movement reaction)

  • Walk-and-turn (heel-to-toe in a straight line)

  • One-leg stand

  • Modified-position-of-attention (feet together, head back, eyes closed for thirty seconds; also known as the Romberg test)

  • Finger-to-nose (tip head back, eyes closed, touch the tip of nose with tip of index finger)

  • Recite all or part of the alphabet

  • Touch each finger of hand to thumb counting with each touch (1, 2, 3, 4, 4, 3, 2, 1)

  • Count backwards from a number such as 30 or 100

  • Breathe into a "portable or preliminary breath tester" or PBT

Although most law enforcement agencies continue to use a variety of these FSTs, a 3-test battery of standardized field sobriety tests (SFSTs) is being being used more and more. These tests are recommended by the National Highway Traffic Safety Administration (NHTSA) after studies indicated other FSTs were relatively unreliable. The NHTSA-approved battery of tests consists of the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg-stand. In some states, such as Ohio, only the standardized tests will be admitted into evidence, provided they were administered and objectively scored "in substantial compliance" with NHTSA standards.

Another type of field sobriety test that is becoming more frequently used involves having the individual breathe into a small, handheld breath testing device. Called either a PAS ("preliminary alcohol screening") or PBT ("preliminary breath test"), the units are small, inexpensive versions of their larger, more sophisticated instruments at the police stations.

Field sobriety tests are better used in determining the level of impairment rather than the Blood Alcohol Content (BAC) of a person.

Chemical Tests:

At the police station, the individual will be offered a chemical test of breath, blood or, sometimes (but not often), urine. Breath test results are usually available immediately. Urine and blood samples are sent to a lab for later analysis to determine the BAC or possible presence of drugs.

Chemical tests are used to determine the driver's BAC but they do not determine the driver's level of impairment.