National Highway Traffic Safety Administration (NHTSA) researchers 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 and these cues fall into four categories:
1) Problems in maintaining proper lane position
2) Speed and braking problems
3) Vigilance problems
4) Judgment problems
The cues presented in these categories can help predict whether a driver is DUI. For example, if an officer observes a driver to be weaving or weaving across lane lines, the probability of DUI is more than .50 or 50 percent. However, if an officer observes either of those weaving cues and any other cue listed below, the probability of DUI jumps to at least .65 or 65 percent.
This is the big giveaway for a DUI. Impaired drivers have an extremely difficult time maintaining proper lane position, most commonly witnesses as weaving. Weaving is when the vehicle alternately moves toward one side of the lane and then the other. The pattern of lateral movement can be fairly regular, as one steering correction is closely followed by another. In extreme cases, the vehicle’s wheels even cross the lane lines before a correction is made. An officer might even observe a vehicle straddling a center or lane line. That is, the vehicle is moving straight ahead with either the right or left tires on the wrong side of the lane line or markers. Drifting, another powerful cue, is when a vehicle is moving in a generally straight line, but at a slight angle to the lane. Indicators of failing to maintain proper lane position include:
Braking properly can be a difficult task for an impaired driver. For example, there is a good chance the driver is DWI if an officer observes any type of stopping problem. Stopping cues include:
Vigilance concerns a person’s ability to pay attention to a task or notice changes in surroundings. A driver whose vigilance has been impaired by alcohol might forget to turn on his or her headlights when required. Similarly, impaired drivers often forget to signal a turn or lane change, or their signal is inconsistent with their maneuver, for example, signaling left but turning right. Alcohol-impaired vigilance also results in motorists driving into opposing or crossing traffic and turning in front of oncoming vehicles with insufficient headway. Cues include”
Operating a motor vehicle requires continuous decision making by the driver. Unfortunately, judgment abilities can be affected by even small amounts of alcohol. For example, alcohol- impaired judgment can cause a driver to follow another vehicle too closely, providing an unsafe stopping distance. Alcohol-impaired judgment also can result in a driver taking risks or endangering others. Cues include:
In addition to the driving cues, the following post-stop cues have been found to be excellent predictors of DUI.