What do police officers look for when attempting to detect drunk driving?

The National Highway Traffic Safety Administration (NHTSA), part of the Department of Transportation, has produced a guide developed during 3 field studies involving hundreds of police officers and more than 12,000 traffic stops, which is entitled “The Visual Detection of DWI Motorists.” This was developed for use by police officers to detect drunk drivers, and most patrol officers have been trained by NHTSA regarding this guide. The guide lists 24 driving behaviors regarded as “cues” for police officers to look for when determining whether make a traffic stop to investigate possible drunk driving. The driving cues are divided into 4 categories: 1) Problems in maintaining proper lane position; 2) Speed and braking problems; 3) Vigilance problems; and 4) Judgment problems. The NHTSA guide claims that the cues presented in these categories predict that a driver in under the influence at least 35% of the time. It also claims that if an officer observes any of the weaving cues and any of the other listed cues, then the probability of driving under the influence jumps to at least 60%. The 24 cues are listed below:

Problems Maintaining Proper Lane Position

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

Speed and Braking Problems

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

Vigilance Problems

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

Judgment Problems

      • Following too closely
      • Improper or unsafe lane change
      • Illegal or improper turn (too fast, jerky, or sharp)
      • Driving on other than the designated roadway
      • Stopping inappropriately in response to officer
      • Inappropriate or unusual behavior (such as throwing items out of the car)
      • Appearing to be impaired (by gripping the wheel too tight, or driving too close to the windshield)
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