DWI Detection

When the police pull you over and investigate you for DWI, they use their training to look for certain things. Their training is based upon the standards set forth by NHTSA. Not all things an officer sees will be related to DWI. For example, speeding, in itself, is not a sign of impairment. Besides being able to read police reports and see all the things that are potential indicators of impairment. It is imperative that your DWI lawyer point out all of the signs of impairment that the officer did not notice.


9. DWI Detection of Alcohol (According to NHTSA)

9.1 DWI Detection Overview

In 1977, in response to an increase in DWI offenses, the government set out to determine what factors an officer can use to determine if someone is impaired. The end product of that research was published. Over the years,  numerous changes were made (yet somehow the manuals refer to the "original research"). Further, three separate validation studies were conducted (four if you include the HGN robustness study).

All New Hampshire police officers should be familiar with the NHTSA DWI detection because it is taught to them at the Police Academy. Proper training is also a pre-requisite to administering the tests post-arrest[1]. The most recent edition of the Student Manual is from 2006. You can usually impeach the officer with the NHTSA manual, or you can try and obtain whatever version the officer was trained by through the New Hampshire State Police Standards & Training, or through a discovery request.


9.2 Phase I Vehicle in Motion (Car Moving)

The first part, or phase, of DWI detection is a vehicle in motion. During this phase, the officer is to observe the driving, to look for certain signs of impairment.

NHTSA has set forth certain things an officer should be looking for.  All of these cues are not equal indicators of impairment. It is interesting to note that for Judgment problems, the predictive reliability rate is 35%-90%. It is hard to imagine any scientific study would allow such a large margin of error. More interesting, the bottom number being 35%, means the officer will be wrong more than he will be correct in using Judgment problems as a sign of impairment.


The officer is or should be looking for the following cues:


9.2.1 Cues while Driving

Problems Maintaining Proper Lane Position[2]

Weaving, weaving across lane lines, straddling a lane line, swerving, turning with wide radius, drifting, and almost striking an object or vehicle (It is puzzling thatalmost striking an object is a cue, but actually striking it is not)


Speed and braking problems[3]

Stopping problems

Accelerating or decelerating rapidly

Varying speed

Slow Speed (10 mph + Under limit)


Practice Note: Speeding, in itself, is not a sign of impairment. It takes greater coordination/mental and physical faculties to control a vehicle that is traveling faster. Some officers believe speeding is a sign of impairment. In my view, they are incorrect.


Vigilance problems[4]

Driving in opposing lanes or wrong way on one-way street

Slow response to traffic signals

Slow or failure to respond to officer's signals

Stopping in lane for no apparent reason

Driving without headlights at night

Failure to signal or signal inconsistent with action (I guess every time you see a police officer not using a turn signal there is a 55%-65% chance he is impaired)


Judgment problems[5]

Following too closely

Improper or unsafe lane change

Illegal or improper turn (too fast, jerky, sharp, etc.)

Driving on other than designated roadway

Stopping inappropriately in response to officer

Inappropriate or unusual behavior (throwing objects, arguing, etc.)

Appearing to be impaired - eye fixation, tightly gripping the steering wheel, slouching in the seat, gesturing erratically or obscenely, face close to windshield, driver's head protruding from vehicle. (Good thing the government spent money on research to conclude appearing to be impaired is a sign of impairment)


9.2.2 Post Stop Cues[6]

Difficulty with motor vehicle controls

Difficulty exiting the vehicle

Fumbling with driver’s license or registration

Repeating questions or comments

Swaying, unsteady, or balance problems

Leaning on the vehicle or other object

Slurred speech

Slow to respond to officer/officer must repeat

Provides incorrect information, changes answers

Odor of alcoholic beverage from the driver


9.2.3 The Stopping Sequence[7]

An attempt to flee

No response

Slow response

An abrupt swerve

Sudden stop

Striking the curb or another object


As you can see, there are many cues the officer is looking for (45 by my count). Some of the cues overlap. Often times, a driver will only exhibit a few of these cues. If the driver does 4 things wrong, that means he did 41 things (or 91%) correct.In a Jury Case, it always good to question how a score of above 90% leads someone to failure (The answer is that everyone fails, and the tests are unfairly set-up to make someone fail).


9.2.4 Special Cues for Motorcyclists[8]

There are separate cues for motorcycles.


Excellent Cues (50% or greater probability)

Drifting during turn or curve

Trouble with dismount

Trouble with balance at a stop

Turning problems (e.g., unsteady, sudden corrections, late braking, improper lean angle)

Inattentive to surroundings

Inappropriate or unusual behavior (e.g., carrying or dropping object,urinating at roadside, disorderly conduct, etc.)



Good Cues (30 to 50% probability)

Erratic movements while going straight

Operating without lights at night


Following too closely

Running stop light or sign


Wrong way[9]


9.3 Phase II – Personal Contact (When the Officer interacts with the driver)



Bloodshot eyes

Soiled clothing

Fumbling fingers

Alcohol containers

Drugs or drug paraphernalia

Bruises, bumps, or scratches

Unusual actions (No, I do not know what this means, but I can likely think of thousands of unusual actions the driver did not do)



Slurred speech

Admission of drinking

Inconsistent responses

Abusive Language

Unusual statements



Alcoholic beverages (Keep in mind alcohol itself has no odor)


Cover up odors like breath sprays (Some mouthwash sprays contain alcohol)

Unusual odor (detecting a theme of unusualbehavior, yet?)


Again, if there are only a few indicators, I like to point out the high percentage of things done correctly.


Practice Tip: Note how the officer asks the driver for a driver's license. If the driver listened, and correctly responded, the driver just completed a divided attention test. The same is true of exiting the vehicle, etc.


9.4 Non-Standardized Field Sobriety Tests

The following three tests are in the Student Manual, and sometimes officers will ask the driver to try to do them. There are no specific scoring criteria for these tests. Further, even though NHTSA’s previous research indicated these tests are not accurate enough to be part of the standardized field sobriety test battery, they are still used by some officers.

Whenever an officer has a subject do the tests, I try to object based upon foundation and relevance. However, it usually goes to the weight of the evidence.


9.4.1 Alphabet Test[13]

The alphabet test requires the driver to speak the alphabet. The officer is supposed to start and end with letters other than A-Z to make it more difficult.

I find this test to be the most difficult to argue that an average driver could not do. Often the officer states that someone mumbles a letter or two. If the driver has a speech disorder or medical condition, perhaps this is a reasonable explanation for any "failure" on the alphabet test.


9.4.2 Count Down[14]

This test has the driver count backwards from a fixed point in reverse. Again, to make it more difficult, the officer is not supposed to start or end on 0 or 5.

This test is also difficult, for me at least, to explain away poor performance on. Except, one may still argue this is not a normal thing average drivers do.

Just like the alphabet test, someone who does not speak English as a first language could have a problem doing this test.


9.4.3 Finger Count[15]

This is the most complicated of the non-standardized tests. The officer asks the driver to touch the top of the thumb to the tip of each finger on the same hand while counting up, 1,2,3,4; then to reverse direction on the fingers while counting down, 4,3,2,1.

Again, there is no approved scoring of this test. Often, an officer will testify the driver does not touch the tip of the finger, counts incorrectly, in the wrong order, or the wrong amount of times (typically the cop asks the person to do the test 3 times),

There is ample room for cross examination of this test. Sometimes, people will use the pad of their finger, and an officer will mark them off for not using the tip. Many people refer to the pad of the finger as the tip, and therefore it should be reasonable to do so. Again, this test is not a common thing a driver would ever do. It is somewhat of a confusing test, and an argument could be made that the driver did not understand what to do if the driver deviates from the officer’s standards. Finally, people with certain medical conditions, such as a stroke, multiple sclerosis (MS), or arthritis, may reasonably have trouble with this test.


[1] N.H. RSA 265-A:6

[2]DWI Detection and Standardized Field Sobriety Testing Student Manual 2006 Edition, NHTSA (Hereafter referred to as 2006 Student Manual) at V-4

[3]Id. at V-5

[4]Id. at V-5

[5]Id. at V-6

[6]Id. at V-7

[7]Id. at V-10

[8]Id. at  V-8

[9]Id at V-8

[10]Id at VI-3



[13]Id. at  VI-5

[14]Id. at VI-6

[15]Id. at VI-6