Field sobriety tests are a series of standardized tests conducted roadside by police officers to determine if a driver is impaired by drugs or alcohol. These tests allow officers to evaluate a driver’s coordination, balance, and mental acuity based on their performance of simple tasks. Poor performance can create probable cause for arrest on suspicion of driving under the influence (DUI) or driving while intoxicated (DWI). Here is an in-depth look at the most common field sobriety tests and how they are administered and scored.
Horizontal Gaze Nystagmus Test
The horizontal gaze nystagmus (HGN) test evaluates a driver’s visual tracking ability by looking for involuntary jerking of the eyes. Nystagmus refers to an involuntary oscillation of the eyes that occurs when the eyes gaze peripherally. Alcohol intoxication enhances this effect and causes the eyes to jerk or bounce rapidly instead of maintaining smooth pursuit movement.
To conduct the HGN test, the officer has the driver follow the motion of a stimulus like a pen, flashlight, or finger held about 12-15 inches in front of the eyes. The driver is instructed to focus on the object with their eyes only while keeping their head still. The officer observes how smoothly the eyes follow the object as it is slowly moved horizontally from center to the driver’s left periphery, then right periphery, and back to center.
Clues officers look for in the HGN test:
- Lack of smooth pursuit – jerking or bouncing eyes rather than steady tracking of the object
- Distinct nystagmus at maximum deviation – pronounced jerking when eyes move as far as possible to the side
- Onset of nystagmus prior to 45 degrees – jerking starts before eyes reach a 45 degree angle from forward gaze
The HGN test checks for these clues in each eye separately, allowing for a maximum of 6 possible clues (3 per eye). Research shows that if 4 or more HGN clues are present, there is an 88% likelihood the driver’s BAC is at or above .10%. However, the absence of HGN clues does not definitively indicate sobriety, as some individuals exhibit little or no nystagmus even at high levels of intoxication.
Officer Training and Administration
Administering the HGN test requires specific training, as officers must recognize subtle differences between normal eye movements and slight nystagmus. Minor jerking could happen naturally due to fatigue or medical conditions. Correctly estimating angles and minimum time assessing each eye is also very important.
Per NHTSA guidelines, the HGN test should be conducted with the driver standing, feet together, and arms at their sides. Only a stimulus like a medical penlight should be used, not an officer’s finger due to distance and angle challenges. Officers are taught to complete the HGN test in a systematic, standardized way and to accurately record observations.
Evidentiary Value and Court Admissibility
Although field sobriety tests provide probable cause for arrest, their evidentiary value in court is limited. For HGN testing, some states allow it as evidence of impairment, while others restrict it to only show probable cause. Differences in HGN administration, officer training, and scoring issues have caused debate around reliability. But with proper procedures followed, HGN testing can be a persuasive factor towards guilt when combined with officer testimony and other evidence.
One-Leg Stand Test
The one-leg stand test evaluates balance and coordination by requiring the driver to stand on one leg with arms at their sides while counting out loud for 30 seconds. Police officers demonstrate and explain the test fully beforehand, showing the specific standing position with raised foot about 6 inches off the ground, toe pointed out. Drivers are instructed to count “one-thousand-one, one-thousand-two” and so on until told to stop.
Impairment clues officers look for include:
- Swaying noticeably while balancing
- Using arms to balance or hopping/dropping the raised foot
- Repeating or missing numbers while counting
- Failing to look down and watch the raised foot
- Failing to complete the full 30 seconds
Scoring is based on the total number of clues observed out of 4 possible. Research correlates 2 or more clues as a 65% predictor that BAC is above .10%.
Proper Administration and Training
According to NHTSA standards, officers should fully explain and demonstrate the one-leg stand test before administering it. Drivers must understand they are to stand straight, keep arms at their sides, raise one foot 6 inches off the ground, look at the elevated foot, and count out loud. The officer times 30 seconds.
Ideally, the test should be conducted on a reasonably dry, hard, level, and non-slippery surface. Loose gravel, wet pavement, snow, or an incline could impact performance. An officer continues watching a driver who makes initial mistakes and notes their overall coherence and coordination throughout.
Evidentiary Value in Court
One-leg stand test results can be admitted as evidence of intoxication and impairment if the officer followed proper procedures and scoring. However, DUI lawyers often challenge it if conditions outside the driver’s control affected performance. Overall, the one-leg stand clues, combined with credible officer testimony, provide persuasive evidentiary value towards intoxication when used alongside other field sobriety and chemical breath or blood test evidence.
The walk-and-turn test assesses coordination, short-term memory, balance, and ability to follow directions. Drivers are instructed to take nine heel-to-toe steps on an imaginary straight line, pivot, and take nine heel-to-toe steps back down the line.
Clues officers look for:
- Stepping off the imaginary line
- Using arms for balance
- Failing to touch heel to toe
- Making improper turns or the wrong number of steps
- Losing balance during the turn
- Starting or stopping during the test
Two or more clues indicates a 79% accuracy for BAC levels above .10%, according to NHTSA-sanctioned research.
Standards for Administration
During the demonstration phase, officers must fully explain that steps should be taken heel-to-toe, along an imaginary straight line. Drivers are advised to watch their feet, keep their arms at their sides, count the steps out loud, make a proper turn with small steps, and return heel-to-toe down the line.
For driver safety and proper scoring, the ground should ideally be dry, hard, level, and without traffic or tripping hazards. Officers closely observe for any missteps, balance checks, or discontinuation of the test by the driver.
Admissibility as Evidence
Courts have ruled the walk-and-turn test admissible as evidence of intoxication when standardized procedures are followed. However, certain conditions like bad weather or poor footwear could invalidate the results. Overall, when combined with the officer’s testimony and other standard field tests, the walk-and-turn provides persuasive evidence of impairment.
Finger to Nose Test
The finger to nose test specifically evaluates balance, coordination and mental acuity. Drivers are instructed to stand with their feet together, arms at their sides, head tilted back, eyes closed, and then touch the tip of the nose using the index finger of each hand upon verbal command. This tests the ability to process instructions and accurately move the finger with vision impaired.
Clues of intoxication:
- Inability to accurately touch tip of nose on first attempt
- Using the wrong fingers or wrong hand
- Swaying noticeably or needing to open eyes to maintain balance
- Failing to follow the verbal commands
At least two clues must be present during the finger to nose test for it to indicate impairment at or above .10% BAC. However, it is not validated for accuracy on its own through NHTSA studies. Thus, it is used in combination with other standardized field tests.
Proper Administration and Scoring
During demonstrations, officers should fully explain the stance, eyes closed, head back position. The driver is told they will be verbally instructed to complete the finger to nose touches, alternating hands. The officer watches closely for any body sway, finger mistakes, or failure to follow commands, while timing the evaluation.
The finger to nose test should ideally be done in a safe space with room for the driver to stand and no distractions or noise interference. As a supplemental test, it provides additional clues of impairment when used along with validated sobriety tests.
Evidentiary Value in Court Proceedings
Due to limited validation data, the finger to nose test generally holds less weight as evidence than other standardized field sobriety tests. However, DUI lawyers still often challenge results if testing conditions were suboptimal or no standardized scoring was used. Overall, when performed correctly, it yields reasonably persuasive evidence of impairment as part of a full field sobriety evaluation.
Hand Coordination Tests
Testing hand coordination provides officers additional insight into fine motor skills and mental processing speed. Common hand coordination field sobriety tests include:
- Finger Count Test – Touching fingers in sequence to thumbs upon specific command. Failure to follow instructions demonstrates slowed mental processing and impaired short-term memory.
- Alphabet Recital – Reciting parts of the alphabet from memory tests mental activity needed for driving. Transposing letters indicates a lack of mental clarity.
- Counting Backwards Test – Counting out loud backwards from a number tests mental agility, tracking, and short-term memory. Making mistakes shows impairment.
While these hand coordination tests are not validated or standardized by NHTSA, officers use them to look for further evidence of intoxication. They are simple evaluations of cognitive functioning, but performance can be affected by external factors. Thus, their evidentiary value is limited without rigorous scoring procedures.
Suspect Interviews and Statements
Beyond physical field testing, the dialogue between officer and driver during initial investigation and questioning provides important evidence and context. Signs of impairment may include:
- Slurred, repetitive, confused, or slowed speech
- Difficulty understanding officer questions and directions
- Bizarre responses to basic biographical queries
- Belligerent, uncooperative, or erratic demeanor
- Illogical thought patterns and disjointed stories
Dash camera footage capturing the suspect interview and conversations further proves sobriety levels and mindset. Combined with poor performance on standardized field tests, documented dialogue and behavior creates compelling legal evidence of intoxication.
Chemical Testing in Conjunction with Field Evaluations
Breath, blood, or urine chemical tests to determine BAC are administered after the field sobriety tests. The legal BAC limit nationwide is .08%, but drivers can be convicted based on total evidence even with lower BAC readings. Chemical test results in conjunction with documented clues or failures on standardized field sobriety tests provide solid, damning evidence of DUI/DWI.
Both the field sobriety testing as well as chemical testing play a crucial role in DUI/DWI convictions. The field testing aims to show visible, functional impairment via simple exercises. Chemical tests legally prove intoxication based on BAC science. Using both testing avenues makes for an airtight case against drunk driving charges.
The Comprehensive Evidence Needed for DUI/DWI Conviction
Taken together, the full range of evidence available to officers builds an overall picture of impairment for DUI/DWI charges:
- Initial witnessing of abnormal or dangerous driving
- Driver behavior and demeanor during initial contact
- Performance, clues, and failures on standardized field sobriety tests
- Statements and interview dialogue admissions
- Documented blood, breath, or urine BAC chemical test results
- Dash cam footage confirming impaired state
When all these components align, the sheer preponderance of evidence overwhelmingly proves driver intoxication and supports criminal DUI/DWI conviction. Even skilled DUI defense lawyers would have difficulty countering such extensive documentation of impairment.
That said, mistakes in administration or scoring of standardized field sobriety tests could weaken the case. As could errors in chemical testing procedures or contradictory dash camera footage. Therefore, officers must be thoroughly trained in proper protocols and administering standardized field sobriety tests uniformly and accurately. This ensures the admissibility and strength of this compelling evidence in court.
In conclusion, standardized field sobriety testing provides police officers the opportunity to evaluate visible signs of impairment at the roadside. Based on driver performance on validated sobriety tests, officers gain further probable cause for DUI/DWI arrest beyond just initial driving observations. Combined with additional evidence like suspect interviews, chemical BAC testing, and dash footage, the field sobriety test clues paint a vivid picture of intoxication for prosecutors. Although not foolproof on their own, when administered correctly according to standardized procedures, field sobriety tests are very persuasive evidence for convicting impaired drivers and getting them off the roads.