Grounds to Stop

Unusual or distinctive driving patterns are usually one of the first things that invite the attention of law enforcement in a DUI case. While not necessarily determinative of the issue of whether or not the defendant was impaired, driving patterns are certainly relevant, and must be successfully dealt with by the defense. In fact, there are times when seemingly troublesome driving patterns may actually be helpful for the defense.

The National Highway Traffic Safety Administration, also called NHTSA, part of the Department of Transportation, has done some fairly exhaustive research on the topic of detecting impaired drivers. NHTSA focused on four categories in which they further developed 24 different clues or “driving cues.” The categories are:

  • Problems in maintaining proper lane position
  • Speed and braking problems;
  • Vigilance problems; and
  • Judgment problems.

The most important thing to know about these categories, and the 24 specific driving cues that belong to them, is that this is what law enforcement officers are being trained to spot in the academy. To the extent that the driving pattern in any cases is not one of these top clues, or is, like in the case of speeding, an opposite of one of the clues (driving too slowly), a DUI criminal defense lawyer can either suppress or distinguish the evidence. For example, alcohol is a central nervous system depressant, and slows down the perception and processing of data. That is why driving too slowly is on the list; alcohol slows everything down. In the case of someone who is stopped for speeding, a DUI criminal traffic defense attorney will be able to show that not only is speeding not on the list, but because of the incredibly small number of DUI arrests that are developed from the thousands and thousands of speeding tickets that are given each day, there is no statistical correlation between speeding and impairment. In fact, it can be argued, it takes much more care and skill to be able to pilot a car going fast than it does going slowly.

NHTSA believes that weaving, plus any other clue, means a 65% probability that the driver is impaired, and that any two clues on the list mean at least a 50% probability of impairment. The cues are:


Problems Maintaining Proper Lane Position

  • Weaving
  • Weaving across lane lines
  • Straddling a lane line
  • Swerving
  • Turning with a wide radius
  • Drifting
  • Almost striking a vehicle or other object

Speed and Braking Problems

  • Stopping problems (too far, too short, or too jerky)
  • Accelerating or decelerating for no apparent reason
  • Varying speed
  • Slow speed (10+ mph under limit)

Vigilance Problems

  • Driving in opposing lanes or wrong way on one-way
  • Slow response to traffic signals
  • Slow or failure to respond to officer’s signals
  • Stopping in lane for no apparent reason
  • Driving without headlights at night
  • Failure to signal or signal inconsistent with action

Judgment Problems

  • Following too closely
  • Improper or unsafe lane change
  • Illegal or improper turn (too fast, jerky, sharp, etc.)
  • Driving on other than the designated roadway
  • Stopping inappropriately in response to officer
  • Inappropriate or unusual behavior (throwing, arguing, etc.)
  • Appearing to be impaired.