Standardized Field Sobriety Testing
An overview of the standard battery of field sobriety tests, and how they are scored. This guild covers the Horizontal Gaze Nystagmus (HGN), Vertical Gaze Nystagmus (VGN), Walk and Turn (WAT), and One Leg Stand (OLS) evaluations used by law enforcement to detect impaired drivers.
Horizontal Gaze Nystagmus (HGN) (6 clues, need 4 to arrest)TEST: 3 clues max per eye. 12 passes total (Plus 4 passes for Equal Tracking). The stimulus should be held 12 - 15 " from nose, just above eye level.
CLUES: (1) Lack of Smooth Pursuit (4 passes, 2/eye, 2" each). (2) Distinct and Sustained Nystagmus at Maximum Deviation (4 passes, 2/eye, 2" each, hold for 4" each eye). (3) Onset of Nystagmus prior to 45 degrees.
NOTES: Does the eye move smoothly or jerk? Does eye jerk when moved as far out as possible (no with showing)? As eye moves, does it jerk prior to 45 degrees?
Vertical Gaze Nystagmus (VGN)TEST: Raise stimulus until eyes are elevated as high as possible.
CLUES: Present / Not Present.
NOTES: Presence indicates high dosage of alcohol or other drugs.
Walk and Turn (WAT) (8 clues, need 2 to arrest)TEST: (1) Instruction Stage - Stand with feet heel-to-toe. Keep arms at side. Listen to instructions. (2) Walking Stage - Take 9 steps up. Turn. Take 9 steps back. While counting out loud.
CLUES: (1) Unable to maintain balance. (2) Starts too soon. (3) Stops while walking. (4) Doesn't touch heel to toe (> 1/2 "). (5) Steps off line. (6) Uses arms to balance (> 6" from side). (7) Loses balance on turn or Improper Turn. (8) Wrong # of steps.
NOTES: Inability to complete WAT occurs when someone steps off line 3 or more times, is in danger of falling, or cannot complete test.
One Leg Stand (OLS) (4 clues, need 2 to arrest)TEST: (1) Instruction Stage - Stand with feet together. Keep arms at side. Listen to instructions. (2) Balance / Counting Stage - Raise one leg. Foot 6 inches off ground. Keep raised foot parallel to ground. Count "one thousand one, one thousand two, etc."
CLUES: (1) Sways while balancing. (2) Uses arms to balance. (3) Hops. (4) Puts foot down.
NOTES: Inability to complete the OLS occurs when someone puts foot down 3 or more times, during the 30 second period, or cannot do the test.