Most DWI arrests occur while a person is driving on a street or highway. It is true many DWIs originate in parking lots or while an officer is watching the exit of a bar, but most DWIs are the result of bad driving on the road. Except for the DWI cases where a person is truly intoxicated and "all over the road," typically an officer observes a driver make one or two driving mistakes late at night that leads to a suspicion by the officer. The most common driving mistakes include swerving across the yellow lines, driving onto the shoulder, or speeding. When an officer sees such suspected DWI driving, he or she will begin to take metal notes of any driving errors, even if they are so minor a driver would not be stopped under normal conditions. Good examples would be a rolling stop through a stop sign, failure to signal lane changes, and even braking. The way the officer will use that information at trial is as follows: "Your honor, Jury, I observed the defendant speeding and swerving across the yellow line. It caught my attention because there are so many Bars in the area, so when I saw the defendant not using the turn signal, it made me think he/she was drunk since many DWI drivers -- in my experience -- do not use turn signals." The truth is that most people do not use turn signals, and that has no bearing on whether a person may or may not be drunk.
It is common for a police officer to follow a suspected DWI driver for a short period of time to gauge the driving, especially in areas or times where road traffic is light. Often the officer will pull right behind the vehicle, waiting for that nervousness to kick in when the driver sees the squad car. A normal reaction, whether or not the driver has been consuming alcohol, is to swerve or lose attention for a moment upon noticing the police car -- an action that is sure to be noted in the police report and used as fodder for the DWI charge. Once the officer has enough observations to sustain pulling over the vehicle, the police officer will initiate the overhead lights and sometimes siren. If the driver yet to realize an officer is trailing, the lights and siren will be sure to extract a startled response, again in the form of momentary loss of concentration and possible driving error.
Once the lights are activated and the driver notices, the next big step is a DWI arrest is the stop. Most people are taught to pull over when they notice an officer trying to stop them, but few people are aware that the officer is closely observing "how" the driver pulls over. On a DWI stop, the officer is taking mental notes of how suddenly or slowly the driver pulls over to the curb or shoulder, where they pull over, and whether they are a sufficient distance from either the edge of the roadway or curb. Likewise, if the car is not exactly perpendicular to the curb or roadside, that information will be used to bolster the officer's opinion of DWI. For instance, a possible Officer testifying at the DWI trial could say: "I initiated by overhead lights, and observed the driver swerve her vehicle to the right, almost to the shoulder. She braked suddenly, almost slamming on them, and skidded to the shoulder. The way she stopped her car indicated to me through my experience, that she was having difficultly concentrating -- she pulled the car onto the shoulder at an angle, with the rear end of the car just a few feet from the roadside, in a dangerous manner."
As the officer approaches the suspected DWI driver's car, the officer will continue looking for clues of intoxication. One of the first things the police will do as the driver rolls down the window is check for the smell of alcohol, While alcohol itself has no smell, an officer will testify that an alcoholic drink's flavoring does has a distinct odor, which if present, will be noted in a report. Almost simultaneously with the nose check for odor of alcohol, is the visual inspection of the driver. This includes the driver's immediate appearance (disheveled, sweating) as well as physical demeanor (confused or aloof, dazed, giddy). Also taken into consideration are the driver's eyes, whether red or bloodshot, breath smell, attention, and any flailing about or slumping.
The officer will typically ask for a driver's license and insurance card, but the method by which the driver gathers the requested documents will be under intense scrutiny. The officer will be looking to further his or her DWI suspected conclusion by searching for the driver looking for the documents in several areas (saying he/ she cannot remember where it is located due to DWI alcohol impairment), looking for the driver to fumble or drop the paperwork (loss of coordination as a sign of DWI), or extreme nervousness as consciousness of DWI guilt.
After the officer has the driver's license and other requested documents, the officer will ask the driver to step out of the car. The manner in which the driver exits the vehicle is important; any stumble or slip is sure to be mentioned in the police report as evidence of DWI. Even the slightest touching of the door upon getting out of the driver's seat, or touching the hood or frame of the car can be noted as 'leaning on the car for support due to unsteady gait.'
The officer will then ask the suspected DWI driver to perform a series of physical tests called Field Sobriety Tests or FSTs. These tests are commonly thought to gauge DWI by looking at how an individual performs on the physical tests. The connection between the tests and actual intoxication is thought to be the derived from the inability to divide attention while intoxicated, thereby causing failure or poor performance on the FSTs when intoxicated. For years this myth was taken as fact in the courtroom, until scientific analysis rebuked the data. Apparently, all FST tests, when compared to actual intoxication at 0.08% or more, failed in accuracy except for three specific tests. Those tests are the walk and turn, Finger to Nose Test, One Leg Stand, Silent Count, and the ABC test. Also used by law enforcement to test DWI intoxication, although more physiological than physical, are the Horizontal Gaze Nystagmus, or HGN DWI test.
The DWI Breath test is where an officer asks the driver of a suspected DWI to blow or breath into a device that calculates BAC. The device is sometimes called a Breathalyzer, although several manufacturers assemble and sell various breath test devices. The goal from a law enforcement perspective is to obtain a breath sample, as close to the time of observed driving as possible, in order to attempt to show in court the driver was intoxicated above the legal limit at the time of driving. Breath tests, along with how the breath test device works, is covered more fully in the breath test section of this DWI guide.
Once the officer has had the opportunity to observe all of the above and determines probable cause is met, an arrest for DWI is made, where the defendant is placed in handcuffs and taken to the station for booking and further testing. Since the breath testing devices mentioned above are not very accurate, a police station may wish to test the defendant again, this time using a blood test, another breath test with a larger more stable machine, or a urine test, although many police stations are shying away from urine testing for DWI.