Research-Based Cues Used To Detect Drunk Drivers At Night

Police officers and others know a number of Cues Used To Detect Drunk Drivers At Night, or during the day. Concerned citizens can also use these research-based tips to tell if someone is drunk or otherwise impaired while driving.

Government Guidelines:

The National Highway Traffic and Safety Administration (NHTSA) developed a number of behavioral cues in drivers that suggest a blood alcohol concentration (BAC) of 0.08 or higher. They identified over 100 behaviors but combined them into 24 that fall into four categories:

  1. Problems maintaining lane position
  2. Speed or braking problems
  3. Vigilance problems (obvious inattention)
  4. Judgment problems

Many of the behaviors in those four categories include obvious things like swerving, sudden course corrections, hard stops at intersections, and so forth.

Drunk drivers may well exhibit more of these behaviors in the dark, because of lower visibility. Stop signs and lane markers can be harder to see, especially for an impaired driver. That is why they may stop short, or brake too hard, or suddenly swerve to get back in their intended lane.

Drunk drivers may exhibit more reckless behaviors at night. Driving without headlights is one such behavior. A driver under the influence may also be confused by reduced visibility and end up driving the wrong way, or straddling a lane, or crossing into oncoming traffic while going around a curve.

During and After a Stop:

When an officer suspects a driver of DUI. A drunk driver may stop inappropriately, in the middle of the lane for example or parking at an angle on the soft shoulder instead of stopping parallel to the road. The driver may veer off the road or swerve across the lane markers when the officer’s lights come on. A police officer who initiates a DUI stop will have seen one or more of those behaviors in almost all cases.

The officer will look at the suspects behavior immediately after the stop. A drunk driver will display classic signs everyone knows, such as slurred speech or difficulty handling their wallet and ID card. A drunk driver is also more likely to give confusing or incorrect responses to simple questions, like “Where are you coming from?” or “Have you been drinking tonight?” If you are stopped on suspicion of driving under the influence, the officer will look for those behaviors.

Correlation between Behaviors and Impaired Driving:

The Department of Transportation has issued a law enforcement guide to behaviors spotting DWI. Here is a summary of what they found (percentages are the odds the behavior is the result of a BAC of 0.10 or higher):

  • Straddling a lane divider or center lane marker (65%) – The driver’s inability to stay in their lane is a classic sign of not being fully in control.
  • Appearing to be drunk (60%) – Behaviors like gripping the wheel tightly and leaning in toward the windshield could be caused by other things, but often indicate the driver is drunk.
  • Weaving (60%) – Moving back and forth in the lane repeatedly is a common sign of being impaired due to fatigue, drugs, or alcohol.
  • Not driving on the designated roadway(55%) – Drivers who are half on the shoulder, who drive in the turning lane, or ignore left-turn only lane only are likely to be drunk or otherwise impaired.

Driving too slowly, driving with a tire on the center lane marker or the edge of the lane, and interfering with other traffic are also signs of drunk driving too. About 50% of those behaviors are caused by drunk driving.

Of course the same behaviors can be a result of driver fatigue, simple distracted driving, or prescription drugs. In all cases, the behaviors still produce unsafe driving.

In short, law enforcement officials and concerned citizens can use a number of cues to suggest that a driver is impaired.

If you have been charged with a crime, contact us to discuss the case.