Not Every Police Stop Begins with Suspicion of Impaired Driving 
Police engage in routine traffic stops throughout every day and night. Such stops can be made for any number of reasons. If it is late at night and the officer observes bad driving, they may initiate a stop based on suspicion of “drunk” or “impaired driving.” But this is not always the case. In many instances, the initial stop may be for something different and unrelated. But, as soon as the officer smells alcohol coming from the car or driver, everything changes. For example, traditional police stops are for speeding, expired tags, non-working lights or other vehicle maintenance issues. There are many other examples, but the point is none of these instances give rise to a concern about impaired driving. We have even had clients who were arrested in early morning traffic here in Charlotte. They were involved in an accident where someone else hits them in the rear. They call the police to get a report and end up in handcuffs. Once the officer smells alcohol, an otherwise routine traffic stop becomes a full DWI investigation which almost always results in arrest. From our experience, we appreciate that every aspect of a DUI case must be thoroughly evaluated to see if there may be a legal challenge to the stop, arrest, and breath or blood testing. Charlotte DWI attorney Aaron Lee will carefully examine everything to determine if the State of North Carolina can actually prove you guilty beyond a reasonable doubt. Being charged only starts the defense process. An arrest does not automatically mean conviction.
DWI Investigation Procedures
For those cases where the officer suspects DUI, there is actually a detailed procedure that has been promulgated by the National Highway Transportation Safety Administration (NHTSA). There is a 24 hour course that police undergo and receive a certificate at the end after field training and a written test. Lawyers who defend DWI cases can pay private vendors to receive this same training and certificate. I strongly encourage all DUI defense lawyers to complete this program as it will significantly change the way you approach and cross-examine officers on “reasonable suspicion” and standardized field sobriety testing during trial.
Vehicle in Motion Phase
The first phase of a proper DUI investigation is the “vehicle in motion” portion. During this initial part of the investigation, the officer is tasked with observing a suspect’s vehicle while it is in motion. There are limited opportunities for this phase in a DWI or sobriety checkpoint scenario. But, in the more typical vehicle on the road situation, the officer is specifically looking for up to 24 “pre-stop” clues of impairment. Contrary to public perception, speeding is not a pre-stop clue. Some of the clues are stereotypical of “drunk driving” while others will be surprising. The first category involves difficult “maintaining proper lane position” and includes “weaving” (both within a lane and/or crossing lanes of travel). “Swerving” is certainly to be expected as is “drifting” but so is “turning with a wide radius.” Finally, this category ends with “almost striking another vehicle or other object.” The next category involves “speed and braking difficulties.” Although the term speed is referenced, speeding in and of itself is not a clue of impaired driving. True clues involve “stopping” issues such as too far or short or in a “jerky” manner. This is the only set of clues that can be observed and documented in sobriety or DUI checkpoint cases. Other clues in this category include speeding up or slowing down for no apparent reason as well as significantly varying one’s speed. Finally, there is the observation of excessively slow speed, defined as at least 10 mph below the posted limit. The thought is people who know they are unsafe will instinctively drive more slowly in an attempt to “drive better” and not draw the attention of police.
Driving Vigilance
The next category deals with “vigilance problems” and includes such issues as driving the wrong way or in an opposing lane of traffic, slow response to traffic signs or signals, stopping for no obvious reason, and/or failure to use signals or using signals improperly. Another set of clues that can be used at checkpoints include slow response or failure to respond to officer commands and driving without headlights at night. We have had a number of cases where our clients tell us they relied on “automatic” headlights to engage but that the car did not given the brightness of street lights in the Charlotte area. Certainly, such explanation seems reasonable but still give the police a reason to stop the vehicle. The final area of pre-stop clues involve “judgement” difficulties and include some of the more expected behaviors. Following too closely, improper lane change, improper turns, and/or driving off the designated road. Others, not so familiar, include stopping inappropriately to an officer and two “catchalls” of (a) unusual behavior (such as throwing things or being argumentative with the officer) and (b) appearing to be impaired (this vague term can mean almost anything by design).
Articulable Suspicion 
At this point, all debate about reasonable suspicion effectively ends. The arresting officer should be able to sufficiently “articulate” what led him or her to reasonably believe they had a legal basis to stop your vehicle. As you might guess, there are seemingly endless scenarios that can be offered to justify a stop. Some stops are based on an immediate suspicion of impaired driving while others are just routine traffic stops that become a DWI investigation once the officer observes an indication of drinking and/or impairment. The only “reasonable suspicion” criteria that does not pass judicial review is illegal “profiling” which cannot survive scrutiny if present. Some might argue that certain “profiles” are reasonable and often lead to arrests based on “hunches.” However, we do not want to live in a society where you can be stopped simply based on racial or other inappropriate basis. Once the first legal hurdle of reasonable suspicion is met, the next analysis is whether the officer developed proper probable cause to arrest. We discuss that issue in more detail on a separate page of this website.