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The Anatomy Of A DUI Investigation

The Anatomy of a DUI Investigation

Attacking the Walk-and-Turn and One-Leg Stand Standardized Field Sobriety Tests

We hear in the news all the time that someone has been convicted of Driving Under the Influence, or DUI. But what types of evidence does the government use to try to obtain a conviction?

To a considerable extent, a conviction for DUI turns on the adequacy of the police investigation and the quality of evidence it produces.

Usually, it starts with a traffic stop. If the officer smells the odor of an alcoholic beverage or detects slurred speech or bloodshot eyes, this is the “reasonable cause” to detain the driver for a road-side investigation into whether the driver was DUI.

During a DUI investigation, the officer employs a series of standardized field sobriety tests to aid in detecting whether the driver is impaired due to alcohol.

Standardized field sobriety tests, when administered properly, have been validated in scientific studies as reliable indicators of whether someone is too impaired by alcohol to safely drive a vehicle. BUT the tests are only reliable IF they are administered properly.

The standardized field sobriety tests used by law enforcement include the Horizontal Gaze Nystagmus (HGN) test, the Walk-and-Turn test, and the One-Leg Stand test.

Of the three standardized field sobriety tests, two are considered divided attention tests: The Walk-and-Turn and One-Leg Stand.

The key here is to understand the clues the officer is looking for during these tests as well as whether the tests are being performed in a standardized manner.

It is essential that the officer carry out these tests out correctly! These tests are supposed to be administered in a very specific way. They are called standardized field sobriety tests for a reason, and therefore they must be performed in a very specific manner.

If not, the officer has not done what he or she was supposed to do in the administration of these tests, making the test result invalid and unreliable. The reason is because the clues cannot be considered as evidence of impairment because the officer did not do what he was required to do

Instructions and Clues of the Walk-And-Turn Test

The officer is looking for eight clues during this test:

Clues During Instructions

  1. Cannot maintain the starting position while listening to the instructions
  2. Starts performing the test before the officer finishes giving instructions

Clues During Performance

  1. Stops walking for several seconds during the test
  2. Does not touch heel-to-toe
  3. Steps off the line
  4. Uses arms to balance
  5. Turns improperly at the end of the first nine steps
  6. Takes the incorrect number of steps either up or down the line

Instruction Stage

The officer begins his instructions by telling the driver to place his left foot on a line, whether that line is real or imaginary, and to touch the heel of his right foot to the toe of his left foot.

The officer must tell the driver to put his arms down by his sides and maintain this position until the officer gives the instruction to start the test.

The officer is supposed to tell the driver as soon as he gets into starting position, “Do not start to walk until told to do so.”

On video if the officer fails to tell the suspect (1) to maintain the starting position or (2) to not begin until told to do so, then indicating either of those clues is without merit.

The failure to follow instructions is dependent on the instruction being given.

The officer continues his instructions by telling the suspect that the test consists of taking nine heel-to-toe steps down the line, turning by making a series of small steps, and then taking nine heel-to-toe steps back up the line.

The officer should tell the suspect not to stop walking during the test. The officer will say, “Do you have any questions? Do you understand what I told you?”


During the instruction stage the officer should demonstrate the test by taking three steps up the line, turning, and taking three steps back down the line. This demonstration is essential to correct instruction on the Walk-and-Turn, and is particularly important for the turn.

The turn looks ridiculous and nobody turns in day-to-day life the way they are instructed to during the Walk-and-Turn. The driver is supposed to be instructed to end the nine steps on their left foot, and then pivot around on that left foot by making a series of small steps with their right foot.​

Without the officer giving a combination of a visual demonstration and detailed instructions, it would be unrealistic to expect someone to make a correct turn during the test.

Testing Stage

Once the driver begins the actual test, the officer is looking for six clues.

If the driver misses one single heel-to-toe step of the eighteen he takes, then the officer notes this as a clue of impairment. If the driver steps off of the line on a single step of the eighteen he takes, then the officer notes this as a clue of impairment.

Stopping while walking would be another clue because the driver was instructed not to stop. Using his arms for balance or raising his arms more than six inches away from his side is another clue.

Many officers note this clue, even if the arms are only slightly off of the person’s body so make sure to ask how far off the body the arms were if this clue is indicated on the DWIR.

The One-Leg Stand Test

  • During the test the officer looks for four clues:
  • Swaying
  • Using arms for balance
  • Hopping
  • Putting the raised foot down

There are no clues to this test during the instructions stage.

The officer should begin by instructing the person to stand with his feet together, arms by his sides, and to maintain that position while the officer gives further instructions. The officer is trained to instruct the driver to raise one foot – the driver is given the discretion on which foot to raise – six inches off the ground and keep it parallel to the ground, while keeping the other leg straight and keeping his arms by his sides.

In addition to the physical portion of the test, the driver is instructed to count out loud, “one thousand and one, one thousand and two, one thousand and three,” and so on, until instructed to stop by the officer.

The officer should ask the driver if he understands the instructions that have been given before telling the driver to begin the test. The officer should also demonstrate how to perform the test in addition to giving verbal instructions.

The officer is trained to time this test for 30 seconds from the time that the driver raises his foot off of the ground. Regardless of whether the suspect gets to “one thousand and ten” or “one thousand and fifty” during his count, the officer is supposed to stop the test at 30 seconds.

Research shows that even a non-impaired driver will have problems maintaining this position for longer than 30 seconds. It is important to limit the test to 30 seconds so that the clues pointing toward impairment will be accurate.

The clues above are the only four clues that have been identified from the test by NHTSA. Failing to count out loud is not a clue.

Missing a sequence in the count, such as jumping from one thousand and four to one thousand and six, is not a clue. Also, each clue only counts once even if the officer sees that clue multiple times during the test.

Limitations of the Walk-and-Turn and One-Leg Stand Tests

Attacking the divided attention tests includes addressing any applicable circumstances where NHTSA has indicated the tests would be inappropriate, including:

  • Age – NHTSA has identified that individuals 65 and older have difficulty performing these tests due to age. For a client who is 60+ you could also indicate that even though administration of the test is allowed, the person is nearing the age where the test results would not be meaningful and that should be taken into account.
  • Location of tests – These tests are to be performed on a reasonably dry, hard, level, and non-slippery surface. If the tests are performed on a hill, a steep grade, in the rain, or in a gravel parking lot with uneven terrain, a false positive for certain clues could result.
  • Weight – A person 50 pounds overweight will likely have difficulty performing the one-leg-stand, according to NHTSA research.
  • Injuries – A person with back, leg, or inner ear problems will have difficulty performing either test. An officer should identify and make note of any medical concerns that are present. However, officers frequently ask “do you have any physical limitations that would prevent you from performing field sobriety tests?” before they instruct a driver on the individual tests. Since most people have never done a field sobriety test, they normally say they are not aware of anything that would keep them from performing the test. If the officer is conducting a fair investigation, he should ask, “do you have any medical concerns related to your legs, back, or inner ear?” Asking someone “can you walk?” is not the same asking them “have you had medical issues with your legs?” Someone who answers the former question “yes” may still be a poor candidate for these tests.
  • Footwear – Any person wearing footwear with two-inch (or higher) heels should be given the option to remove footwear before performing these tests. However, performing the tests barefoot could create additional reasons why an individual might have trouble performing the tests to the satisfaction of the officer.

Challenging the Results of Standardized Field Sobriety Tests

Attack inadequate instructions. For example, “So you never told my client not to begin the Walk-and-Turn before finishing your instructions?”

Attack incorrect test interpretation, i.e. clue noted when it should not have been. For example, “So you say my client used his arms for balance, but he barely raised his arms, not six inches as required by NHTSA?”

Attack the officer who incorrectly finds non-compliance with instruction as a clue of the test. “So you stated that my client exhibited the clue of not counting his steps out loud during the Walk-and-Turn test, but that is not one of the eight clues identified by NHTSA during that test, is it?”

During cross-examination, begin with questions about the particular stages of the SFSTs such as, “How did you instruct my client to perform the One-Leg Stand Test? Tell me exactly how you instruct somebody to perform that test? Are there any other instructions that you give during that test?”

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