What Police Look for During a DUI Stop in Arizona

Jun 8

Most people assume that if someone is stopped for DUI, the driver must have been driving dangerously or obviously intoxicated. In reality, many DUI investigations in Arizona begin with ordinary driving behaviors that sober drivers engage in every day.

That surprises a lot of people.

As a Tucson DUI defense attorney, I regularly review body camera footage, police reports, dash camera videos, and forensic evidence in DUI cases throughout Pima County. One thing that becomes clear very quickly is that not every traffic violation—or even unusual driving behavior—is necessarily a sign of impairment.

Understanding what officers are trained to look for during a DUI investigation can help drivers better understand how these cases begin and why DUI allegations are often more complicated than they initially appear.

How DUI Investigations Usually Start

Most DUI cases begin with a traffic stop. Before an officer can investigate a driver for DUI, the officer generally needs a lawful reason to stop the vehicle.

Sometimes that reason is straightforward, such as:

speeding,
failing to maintain a lane,
running a red light,
driving without headlights,
or committing another traffic violation.

Other times, the officer may describe driving behaviors that they believe are consistent with impairment.

Importantly, not every driving behavior has the same scientific value when it comes to predicting intoxication.

The Difference Between “Bad Driving” and DUI Driving

The National Highway Traffic Safety Administration (NHTSA) has published studies identifying certain driving behaviors that may correlate with impaired driving. Officers often receive training based on these materials.

Some driving cues are considered more strongly associated with impairment than others.

For example, officers may look for:

drifting across lane lines,
nearly striking objects,
stopping far beyond a stop line,
driving significantly below the speed limit,
delayed reactions,
or obvious inability to maintain control of the vehicle.

But many DUI investigations begin with much less dramatic observations.

In fact, behaviors like speeding or weaving within a single lane are not necessarily strong indicators of impairment standing alone.

That matters.

Many sober drivers speed unintentionally. Many drivers drift slightly within their lane while adjusting the radio, speaking to passengers, checking mirrors, driving while tired, or navigating unfamiliar roads.

The reality is that human driving is not perfect.

“Weaving Within the Lane” Does Not Automatically Mean DUI

One phrase that appears frequently in DUI reports is “weaving within the lane.”

People often assume this means the vehicle was swerving dangerously across traffic lanes. Sometimes that is not the case at all.

“Weaving within the lane” may simply refer to minor movement inside a single lane of traffic without actually crossing lane lines.

That distinction is important because ordinary drivers frequently make small steering corrections while driving. Wind, road conditions, distractions, fatigue, nervousness, and even natural driving habits can contribute to these movements.

Jurors often expect DUI driving to look extreme. In many cases, however, the driving observed by police may appear relatively normal on video.

This is one reason body camera and dash camera footage can become critically important in Arizona DUI cases.

What Happens After the Stop

Once a vehicle is stopped, officers begin evaluating the driver for signs of impairment.

Common observations may include:

odor of alcohol,
bloodshot or watery eyes,
slurred speech,
fumbling with documents,
difficulty exiting the vehicle,
swaying,
confusion,
or balance problems.

Some of these observations are subjective.

For example, nervousness can sometimes be interpreted as impairment. So can fatigue. A driver who is upset, anxious, embarrassed, frustrated, or intimidated during a police encounter may not appear perfectly calm or polished on camera.

That does not necessarily mean the person is impaired.

Field Sobriety Tests in Arizona

Officers may also ask drivers to perform field sobriety tests (FSTs).

These tests are designed to help officers look for possible signs of impairment. Common examples include:

the Horizontal Gaze Nystagmus (HGN) test,
the Walk-and-Turn test,
and the One-Leg Stand test.

Many people do not realize that these roadside tests are voluntary in Arizona.

Another important point is that field sobriety tests are not simple “pass/fail” tests. They are divided-attention exercises interpreted by the officer conducting them.

Environmental conditions can affect performance significantly, including:

uneven pavement,
flashing lights,
anxiety,
physical limitations,
injuries,
age,
fatigue,
and footwear.

In some cases, people decline field sobriety testing entirely. Jurors should understand that declining voluntary tests does not automatically establish guilt.

Blood and Breath Testing

If officers believe they have probable cause for DUI, the investigation may continue with breath or blood testing.

Arizona has strict DUI laws, including the well-known .08 blood alcohol concentration threshold. However, DUI cases are often more complicated than a single number on a lab report.

Timing issues, rising alcohol levels, laboratory procedures, medical conditions, human error, and other factors can become important issues in certain cases.

Additionally, impairment and blood alcohol concentration are not always identical concepts under Arizona law.

That is why careful review of all evidence—not just the chemical test—is important.

Why Video Evidence Matters

Modern DUI cases frequently rise or fall based on video evidence.

Body camera footage may allow jurors to independently evaluate:

speech patterns,
coordination,
demeanor,
balance,
responsiveness,
and driving behavior.

Sometimes the video strongly supports the officer’s observations. Other times, the footage may appear inconsistent with the written report.

That does not automatically mean anyone acted dishonestly. Human beings can perceive the same interaction differently, especially during stressful or rapidly developing situations.

But it does reinforce an important principle of our justice system: accusations alone are not evidence.

DUI Charges Do Not Equal Guilt

Many people assume that an arrest means the case is already proven.

That is not how the American legal system works.

An arrest simply means the officer believed there was probable cause to investigate or charge a crime. The State still carries the burden of proving guilt beyond a reasonable doubt.

That burden matters because DUI investigations often involve subjective observations, imperfect human judgment, and complex scientific evidence.

Every case deserves careful review.

DUI Defense in Tucson and Pima County

If you have been charged with DUI in Tucson, Oro Valley, Marana, Sahuarita, Green Valley, or elsewhere in Pima County, it is important to understand that DUI cases are rarely as simple as they first appear.

An experienced Arizona DUI defense attorney can evaluate: