Phase One: Vehicle In Motion

This week St. Charles DWI lawyer Todd Ryan discusses Phase One of the DWI investigation process. In Phase One, the law enforcement officer is observing the driver’s vehicle in motion. Traffic stops that lead to DWI arrests begin under a variety of circumstances, and it’s important for drivers to know how law enforcement officers interpret actions on the road.

In any DWI stop, a driver has caught the officer’s attention due to any number of seemingly innocuous traffic violations, such as failing to signal a turn, going a few miles over the speed limit, or operating a vehicle with expired plates.

Once the officer’s attention is drawn to the driver, he or she is trained to start gathering as much incriminating information as possible. At this point, the officer may do one of three things: 1) stop the driver; 2) continue to observe and investigate; or 3) disregard the driver and move on.

Building upon the previous NHTSA study, researchers interviewed officers from across the United States and developed a list of more than 100 driving cues that have been found to predict blood alcohol concentrations (BAC) of 0.08 percent or greater. The list was reduced to 24 cues during three field studies involving hundreds of officers and more than 12,000 enforcement stops. The driving behaviors identified by the officers are presented in the following four categories: 1) Problems in maintaining proper lane position 2) Speed and braking problems 3) Vigilance problems 4) Judgment problems
The Visual Detection of DWI Motorists

NHTSA’s The Visual Detection of DWI Motorists trains officers to observe various cues and score them using a weighted system. There are five categories of cues: failing to maintain proper lane position; speed and braking problems; lack of vigilance; judgment errors; and post-stop cues.

Proper Lane Position

As we saw in our previous posts on the SFSTs (Walk & Turn, One-Leg Stand), a prominent part of a DWI investigation is observing a driver’s ability to accomplish divided attention tests. A driver must maintain lane position and general speed, but these tasks obviously become more difficult when a driver is impaired.

Officers are trained to look for weaving, drifting, swerving, turning with an excessively wide radius, or almost striking an object or vehicle. Each of these cues involve some form of delayed or unreasonable course correction. Of course, none of these cues are necessarily indicative of impairment, but NHTSA research suggests that there is an increased chance of impairment when one or more of these cues are observed.

Speed & Braking Problems

The second category of impaired driving cues officers are taught to look for is speed and braking problems. Speed and braking are divided attention tasks for drivers, and NHTSA research suggests that stopping too far from a curb or at an inappropriate angle; stopping too short of a limit line or past a limit line; and jerky or abrupt stops are all cues of impairment.

Officers are also taught to determine if drivers are having difficulty maintaining speed. If an officer observes a driver accelerating or decelerating rapidly for no apparent reason; appearing to be speeding up or slowing down in odd intervals; or driving excessively slow (i.e. 10 miles per hour under the speed limit), there is an increased likelihood of the driver being impaired.

It’s important to note that many of the cues described above are not necessarily violative of any traffic law, but drivers should be aware a traffic violation isn’t required for a DWI investigation.

Lack of Vigilance

NHTSA defines vigilance as “concern[i] a person’s ability to pay attention to a task or notice changes in surroundings.” A driver exhibiting problems with vigilance may forget to turn on headlights at night or windshield wipers when conditions call for them. Vigilance problems also result in drivers failing to signal turns, ignoring traffic lights, or even driving the wrong way on a roadway.

As we saw with the SFSTs (Walk & Turn, One-Leg Stand), a key component of impairment is being unable to adequately perform divided attention tests. Over the years at the Ryan Law Firm, there has been an increase of technology-related distracted driving cases that lead to DWI arrests. Drivers are always well served to avoid distractions when driving.

Errors in Judgment

While vigilance more or less concerns a driver’s ability to pay attention to his or her surroundings, judgment problems usually concern a driver’s affirmative choices. Drivers exhibiting problems with judgment may be traveling too fast for current conditions or failing to appreciate their speed — or the speed of oncoming traffic — when turning. NHTSA research suggests that any indication of inappropriate or unusual behavior increases the chance that a particular driver is impaired.

The Ryan Law Firm

415 N. Second St.
St. Charles, Missouri 63301

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