If you are pulled over on suspicion of driving while intoxicated (DWI) in New Jersey, there is a strong chance the officer will ask you to perform field sobriety tests. These roadside exercises are often presented as scientific tools that determine whether a driver is impaired. But what do these tests actually measure? And how reliable are they?
Under New Jersey law, field sobriety tests are commonly used by law enforcement to help establish probable cause for DWI arrest. However, they are not foolproof, and many factors unrelated to alcohol can affect performance.
Understanding how these tests work can help you better understand your rights and how DWI cases are evaluated in New Jersey.
What Are Field Sobriety Tests?
Field sobriety tests (FSTs) are physical and cognitive exercises administered by police officers during a traffic stop. They are designed to assess balance, coordination, attention, and the ability to follow instructions, skills that officers claim are impaired by alcohol or drugs.
The three most commonly used standardized field sobriety tests include:
- Horizontal Gaze Nystagmus (HGN)
- Walk-and-Turn Test
- One-Leg Stand Test
These tests were developed with guidance from the National Highway Traffic Safety Administration (NHTSA), and officers are trained to administer them in a specific manner.
What Do Officers Claim These Tests Measure?
Police officers use field sobriety tests to look for “clues” of impairment. Each test is intended to measure specific physical or neurological responses.
Horizontal Gaze Nystagmus (HGN)
The HGN test measures involuntary jerking of the eyes as they move from side to side. Officers claim that alcohol consumption can exaggerate this jerking.
During the test, the officer asks the driver to follow an object (usually a pen or finger) with their eyes while keeping their head still. The officer looks for certain signs of abnormal eye movement.
Walk-and-Turn Test
This is a divided attention test. The driver must walk heel-to-toe along a straight line, turn in a prescribed manner, and walk back. Officers observe balance, coordination, and the ability to follow instructions.
One-Leg Stand Test
In this test, the driver must stand on one leg while counting aloud for a specified period. Officers look for swaying, hopping, putting the foot down, or losing balance.
Police claim these exercises test both mental and physical abilities that may be impaired by alcohol.
Field Sobriety Tests Are Not Required in NJ
It’s important to understand that in New Jersey, field sobriety tests are generally voluntary. Unlike breath testing under implied consent laws (which may carry penalties if refused after arrest), roadside field sobriety exercises are not mandatory.
However, refusing to perform them may still lead the officer to make an arrest if other signs of impairment are present.
Why Field Sobriety Tests Can Be Unreliable
While officers present FSTs as reliable indicators of intoxication, many factors unrelated to alcohol can impact performance.
Nervousness and Anxiety
Traffic stops are stressful. Even completely sober drivers may feel anxious, intimidated, or shaken—especially when standing on the side of a busy road with flashing lights behind them.
Nerves alone can affect balance, coordination, and the ability to focus.
Medical Conditions
Certain medical issues can significantly impact field sobriety test performance, including:
- Inner ear disorders
- Balance problems
- Neurological conditions
- Knee, hip, or back injuries
- Arthritis
- Obesity
For example, someone with a knee injury may struggle to perform the one-leg stand, even if they have consumed no alcohol.
Age and Physical Fitness
Field sobriety tests may be more difficult for older individuals or those who are not physically agile. These tests were developed based on controlled studies, but not everyone fits the same physical profile.
Weather Conditions
New Jersey weather can create challenging roadside conditions. Snow, ice, wind, rain, or cold temperatures can affect balance and stability.
Attempting to perform heel-to-toe steps on a slippery shoulder or uneven pavement can be difficult for anyone.
Uneven or Unsafe Surfaces
Roadside surfaces are often far from ideal. Gravel, sloped pavement, potholes, and debris can interfere with performance.
Even minor surface irregularities can cause a person to appear unsteady.
Improper Instructions
Officers must administer standardized tests according to specific training guidelines. If instructions are rushed, unclear, or improperly demonstrated, a driver may perform poorly due to confusion, not impairment.
In DWI cases, defense attorneys often examine whether the officer followed proper procedures.
Subjectivity in Scoring
Another concern is that field sobriety tests involve subjective judgment. Officers count “clues” they believe indicate impairment, but interpretation can vary from one officer to another.
Video footage sometimes reveals that a driver’s performance was not as poor as described in the police report. Body camera and dashcam recordings often play a crucial role in challenging FST evidence in court.
How Field Sobriety Tests Fit into a NJ DWI Case
In New Jersey, a DWI charge under N.J.S.A. 39:4-50 may be supported by:
- Officer observations (odor of alcohol, slurred speech, bloodshot eyes)
- Field sobriety test performance
- Breath test results
- Drug recognition evaluations
Field sobriety tests alone do not automatically prove guilt. They are one piece of evidence used to establish probable cause for arrest.
If the case proceeds to court, a defense attorney may challenge:
- Whether the stop was lawful
- Whether the officer properly administered the tests
- Whether medical or environmental factors affected performance
- Whether the officer exaggerated or misinterpreted clues
Breath Tests vs. Field Sobriety Tests
After arrest, drivers may be asked to submit to a breath test. Unlike field sobriety exercises, refusing a chemical breath test in New Jersey can result in license suspension and other penalties under implied consent laws.
Field sobriety tests, however, are preliminary tools. They are often used to justify moving forward with an arrest and breath testing.
The Bottom Line
Field sobriety tests are designed to measure balance, coordination, and divided attention, but they are far from perfect. Anxiety, medical conditions, poor weather, uneven surfaces, and improper instructions can all lead to poor performance, even for sober drivers.
Because these tests are subjective and often administered under less-than-ideal conditions, they can be challenged in court. A DWI arrest based heavily on field sobriety test results does not automatically mean a conviction is inevitable.
If you are facing a DWI charge in New Jersey, understanding how these tests are evaluated is critical to protecting your rights.
Contact Lomurro Law for Experienced NJ DWI Defense
If you were arrested after performing field sobriety tests, you may still have strong defenses available. The outcome of a DWI case can affect your license, finances, and future.
The experienced New Jersey DWI defense attorneys at Lomurro Law carefully analyze traffic stops, field sobriety procedures, and officer conduct to build effective defenses for their clients.
Schedule a consultation and learn how to protect your rights.
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