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DUI enforcement has been around for many years.  Over time, there became a need to develop techniques to aid law enforcement to detect impaired drivers.  But the ways officers worked were as varied as there are law enforcement agencies.  The National Highway Traffic Safety Administration worked to give officers a standardized way to determine if a driver may be under the influence of an intoxicant during a traffic stop or detention.  In so doing, the NHTSA published the DWI Detection And Standardized Field Sobriety Testing manual. Since the initial publication of this manual in 1984, NHTSA has made significant changes throughout the different editions. However, these techniques were only tested to determine the accuracy in only three validation studies in the 1990's. There have been no further studies by either scientists or law enforcement to justify the changes in testing made over time.  

In the original study, six different tests were administered. These included the One-Leg Stand, Finger-To-Nose, Finger Count, Walk-and-Turn, Tracing (a paper and pencil exercise), and Horizontal Gaze Nystagmus.  The researchers concluded that a three-test battery, which included the Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand, offered a reliable field sobriety testing procedure to determine if the subject's blood alcohol level was .10% or greater.  Over time, many stats were gathered about these Standardized Field Sobriety Tests (SFSTs). Statistical analyses indicates that the accuracy of the SFSTs depend on the BAC of the suspect and they may be more useful in identifying subjects with a blood alcohol level substantially greater than the current legal limit of 0.08%.


DUI/DWI stops routinely occur on the sides of roadways and highways.  Therefore, although the SFSTs are "standardized," the testing area can greatly affect the accuracy of these tests.  It doesn't take a rocket scientist to understand that SFSTs conducted on the side of a busy highway at night, with vehicles driving by at varying speeds, with lights flashing and moving, varying weather conditions (cold, wind, etc) will have a much different result than those conducted in the daytime in a closed environment, such as a laboratory. Ideally, the SFSTs should be conducted on a reasonably dry, hard, level, non-slippery surface whenever possible.  However, these conditions are usually not available. 


You have heard it numerous times - no two people are alike.  Every person has different abilities.  Therefore, it is only logical that two people may perform differently on tests such as the One Leg Stand or the Walk and Turn.  One person may have balance problems. Another may be overweight, making it difficult to hold their leg out for a specified amount of time. Yet another may have back problems which make it difficult to walk in a straight line.  These physical limitations will affect the validity of the SFSTs.


Horizontal Gaze Nystagmus (HGN) – Nystagmus is the involuntary jerking of the eye.  there are many causes of nystagmus.  The only reason nystagmus occurs is a neurological impairment.  While this may be caused by the presence of alcohol or drugs in the person's system, false positive observation of alcohol induced nystagmus is not uncommon. In fact, the Court of Special Appeals of Maryland has judicially recognized 3916 non-alcohol related causes of horizontal gaze nystagmus. They include:

  • (1) problems with the inner ear labyrinth;
  • (2) irrigating the ears with warm or cold water under peculiar weather conditions;
  • (3) influenza;
  • (4) streptococcus infection;
  • (5) vertigo;
  • (6) measles;
  • (7) syphilis;
  • (8) arteriosclerosis;
  • (9) muscular dystrophy;
  • (10) multiple sclerosis;
  • (11) Korchaff's syndrome;
  • (12) brain hemorrhage;
  • (13) epilepsy;
  • (14) hypertension;
  • (15) motion sickness;
  • (16) sunstroke;
  • (17) eye strain;
  • (18) eye muscle fatigue;
  • (19) glaucoma;
  • (20) changes in atmospheric pressure;
  • (21) consumption of excessive amounts of caffeine;
  • (22) excessive exposure to nicotine;
  • (23) aspirin;
  • (24) circadian rhythms;
  • (25) acute trauma to the head;
  • (26) chronic trauma to the head;
  • (27) some prescription drugs, tranquilizers, pain medications, anti-convulsants;
  • (28) barbiturates;
  • (29) disorders of the vestibular apparatus and brain stem;
  • (30) cerebellum dysfunction;
  • (31) heredity;
  • (32) diet;
  • (33) toxins;
  • (34) exposure to solvents, PCBs, dry cleaning fumes, carbon monoxide;
  • (34) extreme chilling;
  • (35) eye muscle imbalance;
  • (36) lesions;
  • (37) continuous movement of the visual field past the eyes, i.e., looking from a moving train; and
  • (38) antihistamine use

Despite these varying causes nystagmus, HGN testing is one of the SFSTs. To properly administer this test, the officer must review three factors or “clues” while observing each eye: (1) the ability to follow a slowly-moving object smoothly with the eyes; (2) whether there is distinct and sustained nystagmus in either of the subject's eyes when moved as far as possible to the side (maximum deviation); and (3) and the angle of onset of nystagmus in each of the subject's eyes; i.e., did the nystagmus commence before the eye moved 45 degrees to the side, with the 45 degree angle being determined by the subjective judgment of the officer administering the test.

Walk and Turn In this test, the subject assumes a heel-to-toe stance with the subject's arms down at her side. The subject is to maintain this position until the officer tells her to begin walking. At that time, pursuant to the instructions given by the officer during the instruction phase, the subject is to take 9 heel-to-toe steps down a real or imaginary line (but not necessarily a straight line), turn around and take 9 heel-to-toe steps back up the line. The turn is not a pivot, but instead is made by taking a series of small steps with one foot, keeping the front foot on the line. While walking, the subject is to keep her arms at her side, watch her feet at all times, and count her steps out loud. A suspect is assessed one clue each for the following:

  • (1) cannot maintain balance while listening to the instructions;
  • (2) starts too soon;
  • (3) stops while walking;
  • (4) fails to touch heel-to-toe;
  • (5) steps off the line;
  • (6) uses his or her arms to balance (raises them more than six inches from side);
  • (7) turns improperly; or
  • (8) takes the incorrect number of steps.

Examples of conditions that may interfere with suspect's performance of the walk and turn test include wind and weather conditions; the suspect being over the age of sixty; the footwear of the suspect; and highway traffic.

One Leg Stand  The instructions for this test are given to the subject while the subject stands with her feet together, and arms down at his side until told to start. The instructions which are supposed to be given to the subject (with accompanying demonstration) are for the subject to stand on one leg (either leg), holding out the other foot approximately 6 inches off the ground, foot pointed forward so the raised foot is approximately parallel to the ground. While standing, the subject may be instructed to maintain this position while the officer estimates 30 seconds or the subject may be told to count out loud (one thousand and one, one thousand and two, and so on). Either way, the subject is to keep his arms at his sides at all times and watch the raised foot. Examples of conditions which may impede a suspect's ability to perform this test include a test surface which is not dry and level; the suspect being over the age of sixty; the suspect being at least fifty pounds overweight; footwear which impedes the performance of the test, such as heels; whether the suspect has had sufficient sleep; whether the test is administered at night with lights flashing in the suspect's eyes; whether the weather is cold or hot; and certain medical problems and disabilities.

Non-Standardized Field Sobriety Tests

There are other, non-standardized, field sobriety tests which have been approved for use by such organizations as International Association of Chiefs of Police (“I.A.C.P.”) in their “Improved Sobriety Testing for Boating/Alcohol Enforcement” Student Manual and the U.S. National Park Service. These tests include, but are not limited to:

  • finger to nose test;
  • finger count test;
  • hand pat test;
  • alphabet test;
  • writing/drawing/tracing test;
  • Romberg test;
  • reverse counting test; and
  • coin pickup test.

If you are facing a DUI/DWI charge, contact us immediately for a consultation on your case and your rights.

This web site is designed for general information only. The information presented at this site should not be construed to be formal legal advice nor the formation of a lawyer/client relationship.

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