The Psychology of a DUI Stop

Consider a typical DUI traffic stop that often occurs in Jacksonville, Florida. A police officer will see a person commit a driving infraction such as speeding or running a stop sign late on a Saturday night. The police officer pulls the driver over and immediately suspects the driver of being under the influence of alcohol or drugs, perhaps because of the age of the driver, the fact that it is late on a weekend, the fact that there are certain bars or restaurants down the road or any other factors that may bias the officer. From that point on, the police encounter and the decision as to whether or not to arrest the driver for DUI is very subjective. In other words, whether a DUI arrest is made is not based on concrete, objective factors that can later be confirmed in court; rather, the decision to arrest for DUI will often be based on the perceptions, observations, conclusions and biases of the police officer. Just about every police officer that has made a DUI arrest since the beginning of time will report that the suspect had bloodshot and watery eyes, emitted a strong odor of alcohol, had slurred or mumbled speech and failed the field sobriety tests if the driver submitted to them. However, those conclusions are all very subjective. How bloodshot and watery were the driver’s eyes compared to what they normally look like? What if the driver was in a smoky bar or staring at a computer screen all day? How strong is a “strong odor of alcohol”? What is slurred speech compared to how a person normally speaks? Over the entire time period of the police encounter, how often must the driver slur his/her speech for it to be considered significant? Is the speech slurred due to alcohol or because the person is nervous? How the officer interprets these questions is very subjective.

The word “bias” is not used negatively here but as a natural and normal psychological phenomenon- a cognitive bias, and it is a significant factor. The human brain is wired to see patterns and draw conclusions subconsciously. While we would hope that a police officer would come to a conclusion only after assessing all of the relevant data, humans have a psychological tendency to draw the conclusion and fit the data to conform to that conclusion. The human brain is also wired to avoid conflict. In other words, if we believe something to be true, i.e. we see something we believe conforms to a pattern we assume exists, we challenge ideas or perceptions that are inconsistent with our belief and automatically accept ideas that are consistent with our belief. The human brain is much happier when ideas and perceptions are consistent.

At a DUI stop, if a police officer believes the driver is under the influence of alcohol, i.e. that is the idea he/she perceives that is consistent with the pattern he/she accepts, the officer may interpret the subsequent evidence to conform to that belief. As a result, these subjective factors like bloodshot and watery eyes, slurred speech, an odor of alcohol and performance on field sobriety tests may be interpreted to be consistent with the idea of a drunk driver rather than what the facts actually illustrate.

To simplify, a police officer may have observed people commit traffic violations late on the weekends who turned out to be drunk hundreds of times or more. That officer, as humans are prone to do, will start drawing conclusions based on that experience. The next time that officer pulls a driver over in similar circumstances, his/her brain relates back to prior drivers who were drunk. The pattern is established. We can all relate to the idea that we like to be proven right and we do not like to be proven wrong. It is intellectually uncomfortable to draw a conclusion only to find out it was incorrect. The defense mechanism our brains use to avoid that state of cognitive discomfort forces our brain to see what we want to see, hear what we want to hear and assume what we want to assume to conform to our primary belief- that the driver is driving under the influence of alcohol- even if the facts tell a different story. It is a psychological phenomenon that cannot be denied. As a result, the officer fits this next driver into the pattern that has developed and may interpret the data from the police stop to conform to that pattern and his/her conclusions.

So, what should you do if you are pulled over by a police officer who suspects you of committing a DUI? Well, you cannot fight the instinctual operation of the human brain. You can, however, limit the information you provide to the police officer that can be interpreted unfavorably against you. After you give your name, license, insurance and/or registration, you can politely ask for a lawyer who is familiar with DUI cases in response to any further questions. Keep in mind that anything you say or do can and will be used against you, and when you are dealing with so many subjective factors that are involved in a typical DUI investigation, the less you say and do, the better.

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