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How Do Police Investigate a DWI?

Posted on in DWI

TExas criminal defense lawyerIn local jurisdictions across the country, it is often considered a high priority for police to make arrests for driving under the influence. While laws may vary and terminology may change -- DUI instead of DWI, for instance -- most police officers follow the same procedures for identifying, investigating, and ultimately determining to arrest a driver suspected of being under the influence of alcohol or drugs. So, how do police investigate a DWI?


The National Highway Traffic Safety Administration created the standards and guidelines for DWI investigation and also provide training and instruction materials for police agencies nationwide. According to the DWI Detection and Standardized Field Sobriety Test Manual, a police officer should investigate a DWI in three phases 

Phase One - Vehicle in Motion

Phase one is often initiated when a driver makes an obvious traffic violation. In police training, the infraction might be presented as a driver swerving over the line or speeding. However, there are other noteworthy observations an officer can make like seeing a driver stop abruptly or too early at a stop sign, or driving well under the speed limit. If strange behavior is identified, the officer might follow the vehicle until an infraction is made, so he or she has probable cause to make the stop. 

Phase Two - Personal Contact

Phase two is when the officer initiates contact with the driver as they would during any traffic stop. Police officers are often trained to ask for the required documentation like a driver’s license and insurance card before beginning a soft interview. They may ask about a driver’s whereabouts and activities before driving. At the same time, the officer is also looking for general signs of impairment like slurred speech, bloodshot eyes, or the smell of an alcoholic beverage. If their observations lead them to believe you’re intoxicated, they will then move to phase three. 

Phase Three - Pre-Arrest Screening

Phase three involves the officer administering standard field sobriety tests. The tests include the Horizontal Gaze Nystagmus, Walk and Turn, and the One Leg Stand. In each test, the officer is looking for indicators of impairment. For example, on the HGN, an officer will look for a certain number of eye twitches as you watch a stimulus. If the officer identifies a certain number of clues, the NHTSA guidebook suggests the officer has probable cause to arrest you for DWI. 

Call a Collin County DWI Defense Lawyer 

If you find yourself in a situation where you are being accused of a DWI, remember to follow these 10 tips. And, if you are arrested on charges of DWI in Texas, contact our office immediately. Our Plano, Texas criminal defense attorneys can investigate the circumstances of your DWI arrest and find weaknesses in the prosecution’s case against you.  Call 469-333-3333 for a free consultation today. 




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