Assessing driver’s balance, coordination, and ability to follow instructions
Field sobriety tests are a crucial tool used by law enforcement officers to determine whether a driver is impaired by alcohol or drugs. These tests are designed to assess a driver’s balance, coordination, and ability to follow instructions, all of which can be significantly affected by intoxication. By observing a driver’s performance on these tests, officers can gather important evidence to support their suspicion of impairment and establish probable cause for an arrest.
Gathering evidence of impairment to establish probable cause for arrest
The primary purpose of field sobriety tests is to gather evidence of impairment that can be used to establish probable cause for an arrest. Probable cause is the legal standard that officers must meet to justify taking a driver into custody and charging them with a DUI offense. By documenting a driver’s performance on field sobriety tests, officers can build a strong case that the driver’s ability to operate a vehicle safely was compromised by alcohol or drug use.
Demonstrating driver’s state in court if case goes to trial
In addition to establishing probable cause for an arrest, field sobriety tests can also play a critical role in demonstrating a driver’s impairment in court if the case goes to trial. Officers will typically testify about their observations of the driver’s performance on these tests, using specific examples and clues of impairment to paint a clear picture of the driver’s condition at the time of the stop. This testimony can be powerful evidence for prosecutors seeking to prove beyond a reasonable doubt that the driver was under the influence.
Involuntary jerking of the eyes when following a moving object
The horizontal gaze nystagmus (HGN) test is one of the most widely used field sobriety tests and is considered the most reliable indicator of alcohol impairment. HGN refers to an involuntary jerking or twitching of the eyes that occurs when a person looks to the side at a high angle. This jerking becomes more pronounced and occurs at lower angles when a person is impaired by alcohol.
Onset of nystagmus at lower angles of gaze indicates higher BAC
During the HGN test, the officer will hold a small object, such as a pen or flashlight, about 12-15 inches from the driver’s face and ask them to follow the object with their eyes without moving their head. The officer will look for three specific clues of impairment in each eye: lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees. The earlier the onset of nystagmus, the higher the driver’s blood alcohol concentration (BAC) is likely to be.
Officer checks for lack of smooth pursuit, distinct nystagmus at max deviation
In addition to the onset of nystagmus, officers will also check for lack of smooth pursuit and distinct nystagmus at maximum deviation. Lack of smooth pursuit means that the driver’s eyes are unable to smoothly follow the moving object, instead exhibiting a jerking motion. Distinct nystagmus at maximum deviation refers to a pronounced jerking of the eyes when they are looking as far to the side as possible. The presence of these clues, along with the onset of nystagmus prior to 45 degrees, strongly suggests that the driver is impaired by alcohol.
Divided attention test – requires walking heel-to-toe in a straight line
The walk-and-turn test is another standard field sobriety test that is used to assess a driver’s balance, coordination, and ability to follow instructions. This test is considered a divided attention test because it requires the driver to concentrate on both mental and physical tasks simultaneously. During the test, the officer will instruct the driver to take nine heel-to-toe steps in a straight line, turn around, and take nine heel-to-toe steps back.
Officer looks for loss of balance, wrong number of steps, inability to follow directions
As the driver performs the walk-and-turn test, the officer will be looking for specific clues of impairment. These may include losing balance or stepping off the line, taking an incorrect number of steps, failing to touch heel to toe, using arms for balance, or being unable to follow directions. The officer will make note of any mistakes or difficulties the driver has in completing the test.
Clues of impairment include stepping off line, using arms for balance, improper turn
Some of the most common clues of impairment that officers look for during the walk-and-turn test include stepping off the line, using arms for balance, and making an improper turn. Stepping off the line indicates a loss of balance and difficulty maintaining a straight path. Using arms for balance suggests that the driver is having trouble keeping their body steady and upright. An improper turn, such as pivoting or losing balance during the turn, is another sign that the driver’s coordination and motor skills are impaired.
Balance test – requires standing on one foot while counting aloud
The one-leg stand test is the third standard field sobriety test and is designed to assess the driver’s balance and ability to follow instructions. During this test, the officer will ask the driver to stand with their feet together and their arms at their sides. The driver will then be instructed to raise one foot about six inches off the ground and count aloud, starting with “one thousand one” and continuing until told to stop.
Officer observes for swaying, hopping, putting foot down, inability to count correctly
As the driver performs the one-leg stand test, the officer will observe for specific clues of impairment. These may include swaying while balancing, using arms for balance, hopping to maintain balance, putting the foot down before being told to do so, or being unable to count correctly. The officer will make note of any difficulties or mistakes the driver makes during the test.
Failure to maintain balance or complete test suggests impairment
The inability to maintain balance or complete the one-leg stand test as instructed is a strong indicator of alcohol impairment. Drivers who are under the influence of alcohol often have difficulty keeping their balance on one foot, even for a short period of time. They may sway, hop, or put their foot down repeatedly in an effort to avoid falling over. Failing to complete the test or showing multiple signs of impairment suggests that the driver’s balance and coordination are significantly compromised.
Requires standing with feet together, eyes closed, head tilted back
In addition to the three standard field sobriety tests, officers may also use other tests to assess a driver’s impairment. One such test is the Romberg balance test, which requires the driver to stand with their feet together, eyes closed, and head tilted slightly back. The officer will ask the driver to estimate the passage of 30 seconds in this position, without counting out loud.
Officer looks for swaying, loss of balance, inability to estimate 30 seconds
During the Romberg balance test, the officer will observe the driver for signs of impairment such as swaying, loss of balance, or falling over. The officer will also note whether the driver is able to accurately estimate the passage of 30 seconds. An inability to maintain balance or accurately estimate time can be an indication of alcohol impairment.
Requires touching the tip of the nose with the index finger while eyes closed
Another additional test that officers may use is the finger-to-nose test. During this test, the officer will instruct the driver to close their eyes, tilt their head back slightly, and extend their arms out to the sides. The officer will then tell the driver to touch the tip of their nose with their index finger, alternating between the left and right hand.
Officer checks for missed touch, wrong finger, eyes opening during the test
As the driver performs the finger-to-nose test, the officer will look for clues of impairment such as missing the tip of the nose, using the wrong finger, or opening their eyes during the test. These mistakes suggest that the driver’s coordination, motor skills, and ability to follow instructions are compromised by alcohol impairment.
Cognitive tests to assess mental impairment and ability to follow instructions
In some cases, officers may also use cognitive tests to assess a driver’s mental impairment and ability to follow instructions. These tests may include reciting the alphabet from a specific letter to another, or counting backwards from a given number. While these tests are not as standardized as the three main field sobriety tests, they can still provide valuable information about a driver’s level of impairment.
In addition to field sobriety tests, officers may also use a preliminary breath test (PBT) to help determine whether a driver is impaired by alcohol. A PBT is a small, portable breath test device that can be used in the field to measure a driver’s blood alcohol concentration (BAC). These devices are designed to provide a quick and easy way for officers to gauge a driver’s level of impairment and establish probable cause for an arrest.
During a PBT, the driver will be asked to blow into the device for several seconds. The device will then analyze the breath sample and provide an initial BAC reading. While PBT results are not admissible as evidence of a specific BAC level in court, they can be used to help establish probable cause for an arrest. If the PBT shows a BAC above the legal limit, the officer may use this information, along with other evidence of impairment, to justify taking the driver into custody.
It is important to note that PBTs are not as reliable or accurate as the evidential breathalyzer tests that are typically administered at the police station. PBTs are considered screening devices and are not subject to the same strict calibration and maintenance requirements as evidential breathalyzers. As a result, PBT results are not admissible in court as proof of a specific BAC level. However, they can still be used to support an officer’s probable cause determination and decision to make an arrest.
In most states, drivers have the right to refuse a preliminary breath test without facing additional criminal penalties. Unlike the evidential breathalyzer test, which is typically required under implied consent laws, PBT refusal is not considered a separate offense. This means that drivers who refuse a PBT will not automatically face license suspension or other administrative penalties.
However, refusal may be used to build probable cause and admissible in court
Although drivers have the right to refuse a PBT, this refusal can still be used as evidence to support an officer’s probable cause determination. In some cases, a PBT refusal may actually strengthen an officer’s case for impairment, as it suggests that the driver is trying to avoid providing evidence of their intoxication. Additionally, the fact that a driver refused a PBT may be admissible in court and can be used to argue consciousness of guilt.
As mentioned earlier, one of the key differences between PBTs and evidential breathalyzer tests is that PBT results are not admissible in court as evidence of a specific BAC level. This is because PBTs are considered screening devices and are not subject to the same rigorous calibration and maintenance standards as evidential breathalyzers. While PBT results can be used to establish probable cause for an arrest, they cannot be used to prove a driver’s guilt beyond a reasonable doubt.
Evidential test follows strict procedures and uses more reliable equipment
In contrast to PBTs, evidential breathalyzer tests are administered using more reliable equipment and following strict procedural guidelines. These tests are typically conducted at the police station using a stationary breathalyzer machine that is regularly calibrated and maintained. The officer administering the test must follow a specific protocol to ensure the accuracy and reliability of the results, including observing the driver for a certain period of time before the test to prevent residual mouth alcohol from affecting the results.
Refusal of evidential test often leads to license suspension and other penalties
Another important difference between PBTs and evidential breathalyzer tests is the consequences of refusal. In most states, drivers are considered to have given implied consent to an evidential breathalyzer test as a condition of holding a driver’s license. This means that refusing an evidential test can result in automatic license suspension and other administrative penalties, even if the driver is not ultimately convicted of a DUI offense. In contrast, PBT refusal does not typically carry these same consequences.
If a driver performs poorly on field sobriety tests and/or registers a high BAC on a preliminary breath test, the officer may determine that there is probable cause to make an arrest for DUI. At this point, the traffic stop will transition into a formal arrest process, which involves taking the driver into custody, transporting them to the police station, and completing additional testing and paperwork. In the next section, we will discuss the arrest process in more detail, including the driver’s rights, the booking procedure, and the potential charges they may face.
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