Field Sobriety Tests

In Northern Virginia, the vast majority of DWI arrests in begin with an officer pulling a vehicle over for a perceived driving violation. Upon noticing the smell of alcohol, the officer will then ask the driver (it is important that they ask, not order) to perform a series of field sobriety tests. The sobriety tests have been approved by the National Highway Traffic Safety Administration (NHTSA), and are known as the Horizontal Gaze Nystagmus (HGN), the walk-and-turn test, and the one-legged stand.


During the HGN, a suspect is instructed to follow a flashlight or pen with only their eyes, an officer watching to determine if the suspect’s eye motion is smooth or jerky. Since most judges require an expert to testify to the test’s benefit and value, and an expert usually does not appear in court, the HGN test is not tremendously relevant to DWI cases in Northern Virginia.

Walk and Turn

In the Walk and Turn test, an officer instructs the suspect to stand with one foot in front of the other, touching heel to toe. In Northern Virginia, officers ask defendants to not only establish this position, but to maintain it while listening to the test’s additional instructions. After establishing the initial position, the suspect must then take nine steps in a straight line, which can be either real or imaginary. Lastly, after taking the nine steps, the suspect must pivot. During the Walk and Turn, the officer carefully observes the defendant, looking for any of seven key indicators:

  1. Inability to maintain start position
  2. Starting too early
  3. Stopping to regain balance
  4. The appearance of gaps between feet while taking steps (if the heel actually makes contact with the toe on each step)
  5. Losing balance during the turn
  6. Using arms to maintain balance
  7. Inaccurate number of steps taken

If two or more indicators are present, NHTSA research states that there’s a 79% chance that the driver has a BAC of at least .08.One-legged Stand

In this test, the officer asks the driver to stand on one leg while lifting the other foot six inches off the ground. Once in the position, the driver must count out loud by thousands (one one-thousand, two one-thousand, etc.), while the officer looks for four indicators:

  1. Starting too early
  2. Inability to maintain balance without putting foot down
  3. Using arms to maintain balance
  4. Inability to count accurately

According to NHTSA research, a DWI suspect showing two or more indicators will have a BAC of at least .08 or higher 83% of the time.

Although not specifically NHTSA-approved, there are several additional tests officers could administer, including asking the suspect to count backwards, recite the alphabet, count on their hands or touch their nose with their fingers. Furthermore, the officer could administer a preliminary breath test to determine if a DWI arrest is in order.

Field sobriety tests are often the main factor used to decide whether it was legal for the officer to make a DWI arrest, and are especially important in cases where no blood or breath test was administered. In cases without blood or breath tests, the field sobriety tests will provide the only evidence of intoxication.