There are three phases of DWI or DUI detection: 1) vehicle in motion; 2) personal contact; 3) pre-arrest screening.
This is how police officers identify drunk drivers and gather evidence of DWI or DUI.
Phase One – Vehicle in Motion
Officers are trained to observe the vehicle in operation and note any initial cues of a possible DWI or DUI violation.
Drivers who are impaired often exhibit certain symptoms, including slowed reactions, impaired judgments, impaired vision, and poor coordination.
The National Highway Traffic Safety Administration sponsored research to identify the most common and reliable initial driving indicators of DWI or DUI. This research identified 24 cues, each with an associated high probability that the driver exhibiting the cue is impaired:
2. Weaving across lane lines
4. Straddling a lane line
6. Almost striking object or vehicle
7. Turning with a wide radius
8. Stopping problems (too far, too short, too jerky)
9. Unnecessary acceleration or deceleration
10. Varying speed
11. 10 MPH or more under the speed limit
12. Driving without headlights at night
13. Failure to signal or signal inconsistent with action
14. Driving in opposing lanes or wrong way on one way
15. Slow response to traffic signals
16. Slow or failure to respond to officer’s signals
17. Stopping in lane for no apparent reason
18. Following too closely
19. Improper or unsafe lane change
20. Illegal or improper turn
21. Driving on other than designated roadway
22. Stopping inappropriately in response to officer
23. Inappropriate or unusual behavior
24. Appearing to be impaired
If you exhibit one or more of these, you may be pulled over. Then comes Phase Two.
Phase Two – Personal Contact
The officer will then attempt to gather more evidence of DWI or DUI by observing and interviewing the driver. The officer may also perform some non-standardized sobriety tests on the driver prior to asking the driver to perform the Standardized Field Sobriety Tests.
Officers look for the following specific signs of impairment:
1. Bloodshot eyes
2. Soiled clothing
3. Fumbling fingers
4. Alcohol containers
5. Drug or drug paraphernalia
6. Bruises, bumps, or scratches
7. Unusual actions
8. Slurred speech
9. Admission of drinking
10. Inconsistent responses
11. Unusual statements
12. Abusive language
13. Odor of alcoholic beverages, marijuana, and cover-up odors
Police officers are also trained to use Divided Attention questions and tasks to look for cues. These tactics require the driver to concentrate on two or more things at the same time, e.g.:
1. Asking for two things simultaneously
The officer might ask the driver to produce both his driver’s license and vehicle registration. The officer will then look for the following evidence of impairment:
– forgets to produce both documents
– produces documents other than the ones requested
– fails to see the license, registration, or both while searching for them
– fumbles or drops wallet, purse, license, or registration
– is unable to retrieve documents with fingertips
2. Asking interrupting or distracting questions
The officer might attempt to divide the driver’s attention between searching for the license or registration and answering a new question, such as “What day is it?” or “Where are you coming from?” The officer will then look for the following evidence of impairment:
– ignoring the question and concentrating only on the license or registration search
– forgetting to resume the search after answering the question
– supplies a grossly incorrect answer to the question
3. Asking unusual questions
After obtaining the driver’s license and registration, the officer might ask about your pets or favorite food. The officer might ask a driver’s middle name, but the driver responds by giving his first name. There are many such questions that the driver would normally be able to easily answer, but which might prove more difficult if the driver is impaired, simply because they are unusual questions.
Non-Standardized Sobriety Tests
There are three non-standardized sobriety tests that an officer may ask a driver to perform prior to performing the standardized field sobriety tests.
The driver is required to recite part of the alphabet. The driver is instructed to begin with a letter other than “A” and stop at a letter other than “Z.” Seriously, don’t be afraid to use the alphabet song.
2. Count Down
The driver is asked to count out loud 15 or more numbers in reverse sequence, e.g., from 68 to 53. This test also divides attention because the driver must continuously concentrate to count backwards while trying to remember where to stop.
3. Finger Count
The driver is asked to touch the tip of the thumb to the tip of each finger on the same hand while simultaneously counting up “one, two, three, four,” then to reverse direction on the fingers while simultaneously counting down “four, three, two, one.” This is another divided attention task.
When investigating a DWI or DUI, officers also look at the exit sequence. When an officer asks a driver to exit a vehicle, the officer is trained to look for the following additional specific signs of impairment:
– angry, unusual reactions
– can’t follow instructions
– can’t open door
– leaves car in gear
– “climbs” out car
– leans against car
– keeps hands on car
Now we’re on to Phase Three of DWI and DUI detection.
Phase Three – Pre-Arrest Screening
Officers administer three psycho-physical field sobriety tests: 1) Horizontal Gaze Nystagmus (HGN) Test; 2) Walk and Turn Test; 3) One Leg Stand Test. These tests attempt to simulate the same mental and physical capabilities that a person needs to drive safely:
– information processing
– short term memory
– judgment and decision making
– steady, sure reactions
– clear vision
– small muscle control
– coordination of limbs
1. Horizontal Gaze Nystagmus
The Horizontal Gaze Nystagmus test is administered first, and is considered to be the most reliable of the three standardized field sobriety tests. The police are trained that it is 77% accurate at detecting subjects at or above a 0.10 BAC.
Nystagmus is defined as the involuntary jerking of the eyes. It is a natural and normal phenomenon. Alcohol and certain drugs do not cause this phenomenon, they merely exaggerate or magnify it.
There are over 40 different types of nystagmus and many of them look the same as the Horizontal Gaze Nystagmus that the police are looking for as evidence of DWI or DUI. Most police, however, are not trained to distinguish between the different types, and it is common for an officer to misdiagnose some other form of nystagmus and use it as evidence of DWI or DUI.
Other forms of nystagmus include:
Post Rotational: When a person stops spinning, the fluid in the inner ear remains disturbed for a period of time and the eyes continue to jerk. This is common after a rollover or spin out car accident.
Caloric: When fluid motion in the canals of the vestibular system is stimulated by temperature – cold in one ear and warm in the other. This occurs when the driver’s window is down and the heat is on inside the car.
Optokinetic: When the eyes fixate on an object that suddenly moves out of sight, or when the yes watch sharply contrasting moving images. Examples include watching strobe lights and rotating lights (like the kind on top of the police vehicle), or rapidly moving traffic.
Pathological disorders can also cause misdiagnosed nystagmus.
Procedure for the Horizontal Gaze Nystagmus Test
– Check for eyeglasses. Instruct subject to remove eyeglasses.
– Verbal instructions:
Put feet together, hands at the side;
Keep head still;
Look at the stimulus;
Follow the movement of the stimulus with the eyes only;
Keep looking at the stimulus until told the test is over.
– Position the stimulus 12-15 inches in front of the subject’s nose, slightly above eye level to commence the test.
– Check for equal pupil size and resting nystagmus.
– Check for equal tracking.
– If a person has unequal pupil size, resting nystagmus, or unequal tracking, it suggests the person is likely to have medical conditions or injuries that will cause nystagmus. Some seizure medications also cause nystagmus.
– If the person has an obvious eye disorder or an artificial eye, the HGN test should not be administered.
– Lack of smooth pursuit.
– It is necessary to move the object smoothly in order to check the eye’s ability to pursue smoothly. The stimulus should be move from center position, all the way out to the right side (checking the subject’s left eye) where the eye can go no further, and then all the way back across the subject’s face all the way out to the left side where the eye can go no further (checking the subject’s right eye) and then back to the center.
– The object must be moved steadily, at a speed that takes about two seconds to bring the eye from center to side.
– In checking for this clue, make at least two complete passes in front of the eyes.
– Check the right and left eye for the “Distinct and Sustained Nystagmus at Maximum Deviation” clue.
– Onset of nystagmus prior to 45 degrees
– Total the clues.
Maximum number of clues possible for each eye: 3
Total maximum number of clues for both eyes: 6
– Check for vertical nystagmus
– Position the stimulus horizontally, about 12-15 inches in front of the subject’s nose.
– Instruct the subject to hold the head still, and follow the object with the eyes only.
– Raise the object until the subject’s eyes are elevate as far as possible.
– Hold for a minimum of four seconds.
– Watch closely for evidence of the eyes jerking upward.
– For VGN to be recorded, it must be distinct and sustained for a minimum of four seconds at maximum elevation.
That’s the Horizontal Gaze Nystagmus test, the first of the Standardized Field Sobriety tests used by police to gather evidence of DWI or DUI.
2. Walk and Turn Test
The second test used to detect DWI or DUI is the Walk and Turn test. The original research for this test shows that it is only 68% accurate in determining if a person’s BAC is 0.10 or higher.
The Walk and Turn test should be conducted on a reasonably dry, hard, level, nonslippery surface. There should be sufficient room for subjects to complete the nine heel to toe steps.
Individuals over 65 years old and people with back, leg, or inner ear problems have difficulty performing this test. Other conditions affecting the test results are the subject’s footwear and wind/weather conditions.
People wearing sandals, heels more than two inches high, or any other form of unusual footwear should be given the opportunity to remove their shoes.
For standardization, the subject should assume heel to toe stance and be given the following verbal instructions, accompanied by demonstrations:
Place your left foot on the line (real or imaginary).
Place your right foot on the line ahead of the left foot, with the heel of your right foot against the toe of the left foot.
Place your arms down at your sides.
Maintain this position until I have completed the instructions. Do not start to walk until told to do so.
Do you understand the instructions so far? (Make sure the subject indicates understanding)
Explain the test requirements by giving instructions, accompanied by demonstrations:
When I tell you to start, take nine heel to toe steps on the line, turn, and take nine heel to toe steps down the line.
When you turn, keep the front (lead) foot on the line, and turn by taking a series of small steps with the other foot like this.
While you are walking, keep our arms at our sides, watch your feet at all times, and count your steps out loud.
Once you start walking, don’t stop until you have completed the test.
Do you understand the instructions far? (Make sure the subject indicates understanding)
Instruct the person to begin the test.
There are eight possible clues that can be observed on the test. The person fails the test if two or more clues are observed:
Cannot keep balance while listening to instructions. Feet must actually break apart or step off the line. It is not a clue if a subject simply steps out to ask a question.
Starts too soon. It is not a clue if the subject starts walking before he is given the instruction telling him not to start until he is told to do so.
Stops while waking. The subject stops while walking. Do not record this clue if the subject is merely walking slowly.
Does not touch heel to toe. This is only a clue if the subject leaves a space of more than one half inch between the heel and the toe on any step.
Steps off the line. The subject steps so that one foot is entirely off the line.
Uses arms to balance. The subject raises one or both arms more than six inches from the sides in order to maintain balance. The arms must be raised more than six inches from their natural hang. It is not a clue if the subject raises them for a reason other than to balance.
Improper turn. The subject removes the front foot from the line while turning. Also record this clue if the subject has not followed the directions as demonstrated, e.g., spins or pivots around or loses balance while turning.
Incorrect number of steps. The subject takes more or less than nine steps in either direction.
*Cheat: If you look straight ahead, instead of at your feet, you can see the horizon, which makes the test easier.
That’s the Walk and Turn test, the second of the Standardized Field Sobriety tests used by police to gather evidence of DWI or DUI.
3. One Leg Stand Test
The One Leg Stand test is the last of the Standardized Field Sobriety tests used by police to gather evidence of DWI or DUI.
Original research shows this test is only 65% accurate in determining if a person’s BAC is 0.10 or higher. This test also requires a reasonably hard, level, and nonslippery surface. Again, people over 65 and those with back, leg, or inner ear problems may have difficulty. People 50 or more pounds overweight will also have problems with this test.
Here are the instructions:
Please stand with you feet together and your arms down at your sides, like this.
Do not start to perform the test until I tel you to do so.
Do you understand the instructions so far?
When I tell you to tart, raise either leg, with the foot about six inches off the ground.
Keep both legs straight and your arms at your side.
While holding that position, count out loud in the following manner: “one thousand one, one thousand two, one thousand three,” and so on until told to stop.
Keep your arms at your side at all times and keep watching the raised foot.
Do you understand?
Go ahead and perform the test. Officer should time the test and discontinue the test after 30 seconds.
If the subject puts the foot down, give instructions to pick the foot up again and continue counting from the point at which the foot touched the ground. If the subject counts very slowly, terminate the test after 30 seconds.
There are four possible clue for this test, and observation of two or more means failure:
Sways while balancing. This refers to side to side or back and forth motion while the subject maintains the one leg stand position.
Uses arms for balance. Subject is able to keep one foot off the ground, but resorts to hopping in order to maintain balance.
Hopping. Subject is able to keep one foot off the ground, but resorts to hopping in order to maintain balance.
Puts foot down. The subject is not able to maintain the one leg stand position, putting the foot down one or more times during the 30 second count.
*Cheat: Pointing your toe upward instead of straight and keeping a slight bend in the knee make it easier to balance.
The One Leg Stand test is the last of the Standardized Field Sobriety tests used by police to gather evidence of DWI or DUI.
While this is all great information to have about DWI and DUI, the best advice is to be smart and safe: Don’t drink and drive. Don’t get into a vehicle with a drunk driver. And be watchful for drunk drivers on the roadway.
Jean-Paul Guidry is a Shreveport DWI lawyer.