There are generally three Driving While Intoxicated (DWI) detection phases. Unless there is an accident or the officer comes upon a parked vehicle, Phase 1 is usually the vehicle in motion; Phase 2 of DWI detection is the personal contact phase; and the Phase 3 is pre-arrest screening. In this blog I will discuss Phase 1 – Vehicle in Motion.

The Vehicle in Motion phase involves the officer’s observations of how the vehicle is being operated. In 1997 the National Highway Traffic Safety Administration funded a study which identified specific erratic driving patterns performed those with a BAC in excess of .08. These erratic driving problems include:

Problems Maintaining Proper Lane Position
(1) Weaving
(2) Swerving
(3) Weaving across lane lines
(4) Straddling a lane line
(5) Drifting
(6) Turning with a wide radius
(7) Almost striking a vehicle or other object
Problems with Speed and Braking
(8) Stopping problems (too far, too short, or too jerky)
(9) Accelerating or decelerating for no apparent reason
(10) Varying speed
(11) Slow speed (10+ mph under limit)

Vigilance Problems
(12) Driving in opposing lanes or wrong way on one-way
(13) Slow response to traffic signals
(14) Slow or failure to respond to officers signals
(15) Stopping in lane for no apparent reason
(16) Driving without headlights at night
(17) Failure to signal or signal inconsistent with action
Judgment Problems
(18) Following too closely
(19) Improper or unsafe lane change
(20) Illegal or improper turn (too fast, jerky, sharp, etc.)
(21) Driving on other than the designated roadway
(22) Stopping inappropriately in response to officer
(23) Inappropriate or unusual behavior (throwing, arguing, etc.)
(24) Appearing to be impaired
Studies have shown that there is a 65% probability that the driver is intoxicated if weaving plus one of the other above listed clues are present. If any two cues other than weaving are present the probability that the driver is intoxicated is at least 50 percent. The presence of some cues alone (such as swerving, accelerating for no reason or driving on other than the designated roadway) have probabilities greater than 70 percent.

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