Much of a DWI case is created before the driver ever reaches the police station. The reason for the stop, the officer’s observations, the roadside environment, the instructions given, and the body-camera recording can all affect how the evidence should be evaluated.
The Stop Comes First
A traffic stop is a seizure under the federal and New Jersey constitutions. Police need a lawful basis to stop a vehicle, such as reasonable suspicion of a traffic violation or other unlawful conduct. A DWI case may also begin through a checkpoint, crash investigation, disabled vehicle, or other police contact, and each setting has its own legal analysis.
What Officers Look For at the Roadside
DWI reports often refer to driving behavior, odor of alcohol or cannabis, bloodshot or watery eyes, speech, fumbling with credentials, admissions about drinking or drug use, balance, demeanor, and the driver’s performance on roadside exercises. None of those observations exists in a vacuum.
Body-camera and dash-camera recordings can be especially important because they allow the court to compare the written report with what can actually be seen and heard.
The Three Standardized Field Sobriety Tests
The National Highway Traffic Safety Administration’s standardized battery consists of three tests:
- Horizontal Gaze Nystagmus (HGN): an eye-movement examination.
- Walk-and-Turn: a divided-attention walking exercise.
- One-Leg Stand: a divided-attention balance exercise.
NHTSA’s training materials prescribe specific instructions, demonstrations, clues, and test conditions. The roadside setting matters. Surface, lighting, weather, footwear, age, injury, balance problems, and other physical limitations can affect performance.
HGN Has a Special Evidentiary Status in New Jersey
New Jersey treats HGN differently from ordinary observations of balance and coordination. In State v. Doriguzzi, the Appellate Division held that HGN results were not admissible at trial to prove a defendant guilty of DWI on the record then presented. The result does not mean the officer is forbidden from performing HGN during an investigation, but it does mean the defense should distinguish investigative use from proof of guilt at trial.
Walk-and-Turn and One-Leg Stand Are Not Pass-Fail Games
The standardized tests are designed around particular clues, not a casual conclusion that someone “failed.” A meaningful review asks whether the officer explained and demonstrated the test correctly, whether the driver understood the instructions, which standardized clues were actually observed, and whether the conditions or the person’s physical condition offered another explanation.
Video can cut both ways. It may support the officer’s description, undermine it, or show a more mixed picture than either side’s summary.
Field Sobriety Testing and Probable Cause
Roadside observations and field exercises are often used in deciding whether probable cause existed to arrest for DWI. Probable cause is a lower standard than proof beyond a reasonable doubt. Evidence sufficient to justify an arrest does not necessarily prove the charge at trial.
What the Defense Reviews
The useful comparison is among the report, the officer’s training, the standardized protocol, the actual environment, the driver’s medical or physical circumstances, and the video. The point is not to assume the tests are worthless or infallible. It is to determine what they fairly prove in this particular case.