24 Hour Toll Free Help

What do police look for in a DUI arrest?

Prior to stopping your car, police officers must have “reasonable suspicion” to pull you over. What does this mean? Drivers have rights outlined in the Constitution, the Bill of Rights and their state laws which prevent police from stopping them without a valid reason. If a police officer witnesses an illegal traffic violation they may stop your car and issue you a ticket for the driving violation. It is not uncommon for many drivers to be arrested for DUI after they have been pulled over by law enforcement, but first the officer must establish probable cause for the DUI arrest. Keep in mind, if the police officer did not have a valid reason to pull you over, you may be able to successfully prove that your rights have been violated.

Establishing Probable Cause for DUI Arrest

Establishing probable cause for a DUI arrest may be more complicated than having reasonable suspicion for detaining you to investigate. First, let’s talk about reasonable suspicion. Police officers may establish reasonable suspicion by witnessing any of the following illegal driving actions (list provided by the National Highway Traffic Administration): • Weaving • Straddling the middle lane marker • Turning with too wide a radius • Erratic braking • Driving into oncoming traffic • Drifting into another lane • Stopping and starting without cause • Tailgating • Swerving • Inconsistent signaling • Slow response to traffic lights • Driving with the headlights off at night • Speeding up and slowing down Although reasonable suspicion may be established by these illegal driving actions, the police officer will generally need more evidence of intoxication to arrest you for a DUI. Police officers may use field sobriety testing and breathalyzer tests to establish probable cause which is defined as "a reasonable belief that a person has committed a crime" or "a reasonable amount of suspicion, supported by circumstances sufficiently strong to justify a prudent and cautious person's belief that certain facts are probably true.”

Field Sobriety Tests

Field Sobriety Tests have been standardized throughout the United States and consist of the heel-to-toe walk, one leg stand, and horizontal gaze nystagmus test. The tests could possibly include the following: 1. Horizontal Gaze Nystagmus For this test the police officer will hold a pen (or other object) about twelve inches away from the driver’s face. The officer then slowly moves the object from one side to the other while watching the driver’s eyes. The officer is looking for the eyeball twitching or shaking. This involuntary movement of the eye could indicate that the driver has ingested an intoxicant. The officer is also paying attention to any incriminating statements the driver may make during the test. 2. One leg stand test For this test driver stands with their feet together, arms at their side and they are instructed to lift one leg off the ground while counting. The law enforcement officer is looking for wobbling, swaying, raising the arms, or hopping. Research shows that drivers who demonstrates two or more of these indicators has a 65% chance of having a BAC of at least .10%. 3. Walk and turn test For this test the driver takes nine heel-to-toe steps along a straight line. They then turn, and take nine steps back. What is the office observing? He is observing whether the driver can keep their balance while walking and turning and if they can follow instructions.

Breathalyzer Test

Breathalyzers measure the level of alcohol concentration in the driver’s blood. Alcohol is absorbed through the membranes in a person's mouth, throat, stomach, and intestines and then into the bloodstream. Finally, the alcohol is expelled through evaporation into the driver’s lungs. The alcohol is then released into the driver’s breath. A breathalyzer test allows the blood alcohol concentration of the driver’s blood to be measured. How do you measure a driver’s BAC? The amount of alcohol in 2,100 ml of the driver’s breath is exactly equivalent to the amount of alcohol in 1 ml of the driver’s blood.

Making a DUI Arrest

So how will the police officer establish probable cause? The officer must evaluate the totality of the evidence that they have established through observation, testing and the breathalyzer test. The officer may make the DUI arrest if they have enough evidence that “a reasonable person would believe that an offense has been committed and that the defendant is the one who committed it.” The evidence must also suggest that not only has the driver consumed alcohol, but their driving is impaired by the alcohol, and it is unsafe for them to operate a motorized vehicle.