Indicators of nighttime impaired driving

The National Highway Traffic and Safety Administration (NHTSA) conducted research to determine initial indicators of a DUI.  NHTSA in their February 2006 Edition, DWI Detection and Standardized Field Sobriety Testing, identified 24 “cues”.  When one or more of these 24 cues exists, per the NHTSA at V-2, there is a “high probability” that the driver cue was observed is impaired to the point of being unsafe to drive a motor vehicle.  Please note: all information referenced to “NHTSA” is from their February 2006 Edition, DWI Detection and Standardized Field Sobriety Testing.

I am using the language from NHTSA  and DWI Detection and Standardized Field Sobriety Testing, because law enforcement is trained with this information and book.  I want you, the reader, to see what law enforcement if being told about DUI investigations, because you have more likely than not, been subjected to a DUI related investigation conducted in part based on techniques and procedures attributed to NHTSA.

NHTSA in their above mentioned manual at pages V-3 to V-7 identified the following “cues” that police officers may use to detect nighttime impaired DUI drivers.  NHTSA claims that the “cues” are based on research involving three studies of more than 12,000 DUI enforcement stops.  NHTSA has organized the “cues” into four groups: problems maintaining proper lane position, speed and braking problems, vigilance problems and judgment problems.

Problems maintaining proper lane positions

1.  Weaving: NHTSA definition: “the vehicle alternatively moves toward one side of the roadway and then the other, creating a zig zag course.  The pattern of lateral movement is relatively regular as one steering correction is followed by another.”

2.  Weaving across lane lines: NHTSA definition: “Extreme cases of weaving when the vehicle wheels cross the lane lines before correction is made.”

3.  Straddling a lane line: NHTSA definition: “The vehicle is moving straight ahead with the center or lane marker between the left-hand and right-hand wheels.”

4.  Swerving: NHTSA definition: “A swerve is an abrupt turn away from a generally driven straight course.  Swerving might occur directly after a period of drifting when the driver discovers the approach of traffic in an oncoming lane or discovers that the vehicle is going off the road; swerving might also occur as an abrupt turn is executed to return the vehicle to the traffic lane.”

5.  Turning with a wide radius: NHTSA definition: “During a turn, the radium defined by the distance between the turning vehicle and the center of the turn is greater than normal.  The vehicle may drive wide in a curve.”

6.  Drifting: NHTSA definition: “Drifting is a straight line movement of the vehicle at a slight angle to the roadway.  Drifting might be observed within a single lane, across lanes, across the center divide, onto the shoulder and from lane to lane.”

7.  Almost striking object or vehicle:  NHTSA definition:  “The observed vehicle almost strikes a stationary object or another moving vehicle.  Examples include: passing abnormally close to a sign, wall, building, or other object; passing abnormally close to another moving vehicle; and causing another vehicle to maneuver to avoid collision.”

Speed and braking problems

1. Stopping problems (too far, too short, too jerky): NHTSA definition: “Stopping too far from a curb or at an inappropriate angle.  Stopping too short or beyond limit line at an intersection.  Stopping with a jerking motion or abruptly.”

2.  Accelerating or decelerating rapidly: NHTSA definition: “This cue encompasses any acceleration or deceleration that is significantly more rapid than that required by the traffic conditions.  Rapid acceleration might be accompanied by breaking traction; rapid deceleration might be accompanied by an abrupt stop.  Also a vehicle might alternatively accelerate and decelerate rapidly.”

3.  Varying speed: NHTSA definition: “Alternating between speeding up and slowing down.”

4.  Slow speed (10MPH+ under the limit): NHTSA definition: “The observed vehicle is being driven at a speed that is more than 10 MPH below the speed limit.”

Vigilance problems

1.  Driving in opposing lanes or wrong way on one way street: NHTSA definition: “The vehicle is observed heading into opposing or crossing traffic under one or more of the following circumstances: driving in the opposing lane; backing into traffic; failing to yield the right of way; driving the wrong way on a one way street.”

2.  Slow response to traffic signals: NHTSA definition: “The observed vehicle exhibits a longer than normal response to a change in the traffic signal.  For example, the driver remains stopped at the intersection for an abnormally long period of time after the traffic signal has turned green.”

3.  Slow or failure to respond to officer’s signals: NHTSA definition: “Driver is unusually slow to respond to an officer’s lights, siren or hand signals.”

4.  Stopping in lane for no apparent reason: NHTSA definition: “The critical element in this cue is that there is no observable justification for the vehicle to stop in the traffic lane; the stop is not caused by traffic conditions, traffic signals, an emergency situation, or related circumstances.  Impaired drivers might stop in the lane when their capability to interpret information and make decisions becomes impaired.  As a consequence, stopping in lane for no apparent reason is likely to occur at intersections or other decision points.”

5.  Driving without headlights at night: NHTSA definition: “The observed vehicle is being driven with both headlights off during a period of the day when the use of headlights is required.”

6.  Failure to signal or signal inconsistent with action: NHTSA definition: “A number of possibilities exist for the driver’s signaling to be inconsistent with the associated driving actions.  This cue occurs when inconsistencies such as the following are observed: failing to signal a turn or lane change; signaling opposite to the turn or lane change executed; signaling constantly with no accompanying driving action; and driving with four way hazard flashers on.”

Judgment problems

1.  Following too closely: NHTSA definition: “The vehicle is observed following another vehicle while not maintaining the legal minimum separation.

2.  Improper or unsafe lane change: NHTSA definition: “Driver taking risks or endangering others.  Driver is frequently or abruptly changing lanes without regard to other motorists.

3.  Illegal or improper turn (too fast, jerky, sharp, etc): NHTSA definition: “The driver executes any turn that is abnormally abrupt or illegal.  Specific examples include: turning with excessive speed; turning sharply from the wrong lane; making a U illegally; turning from outside a designated turn lane.”

4.  Driving on other than the designated roadway: NHTSA definition: The vehicle is observed being driven on other than the roadway designated for traffic movement.  Examples include driving at the edge of the roadway, on the shoulder, off the roadway entirely, and straight through turn-only lanes or areas.”

5.  Stopping inappropriately in response to officer: NHTSA definition: “The observed vehicle stops at an inappropriate location or under inappropriate conditions, other than in the traffic lane. Examples include stopping: in a prohibited zone; at a crosswalk; far short of an intersection; on a walkway; across lanes; for a green traffic signal; for a flashing yellow traffic signal; abruptly as if startled; or in an illegal, dangerous manner.”

6.  Inappropriate or unusual behavior (throwing objects, arguing, etc): NHTSA definition: “Throwing objects from the vehicle, drinking in the vehicle, urinating at the roadside, arguing without cause, other disorderly actions.”

7.  Appearing to be impaired: NHTSA definition: “This cue is actually one or more of a set of indicators related to the personal behavior or appearance of the driver.  Examples of specific indicators might include:

eye fixation

tightly gripping the steering wheel

slouching in the seat

gesturing erratically or obscenely

face close to the windshield

driver’s head protruding from vehicle

Post stop cues (per NHTSA)

In addition to the 24 cues involving the observation of how the driver actually drove, NHTSA at page V-7 also indentified ten cues that may be present after the driver stops.

1.  Difficulty with motor vehicle controls

2.  Difficulty exiting the vehicle

3.  Fumbling with driver’s license or registration

4.  Repeating questions or comments

5.  Swaying, unsteady or balance problems

6.  Leaning on the vehicle or other object

7.  Slurred speech

8.  Slow to respond to officer/officer must repeat

9.  Provides incorrect information, changes answers

10.  Odor of alcoholic beverage from driver

NHTSA emphasizes that the effects of alcohol on driving are illustrated in a driver’s inability to perform tasks involving divided attention.  Divided attention, per NHTSA at page V-9, is “the driver’s ability to concentrate on two or more things at the same time.”  An impaired driver tends to focus on only one or more of the many important driving tasks, and either completely disregards other important ones or treats them as being less important than they really are.

Driving is complex, because it involves the performance of many “subtasks” simultaneously, per the NHTSA at pages V-8 and V-9, that include:


controlling the accelerator


controlling the brake pedal

operating the clutch

operating the gearshift

observing other traffic

observing signal lights, stop signs and other traffic control devices

making decision (whether to stop, turn, speed up, slow down)

Cues of impairment per NHTSA at page V-10 may be found in how the driver stops after being signaled to do so by the officer.  These cues may, per NHTSA include:

an attempt to flee

no response

slow response

an abrupt swerve

sudden stop

striking the curb or other object

NHTSA at page V-10 believes that the when police stop a driver, the driver’s attention becomes divided.  To stop a driver, police use sirens, solid and flashing lights, as well as verbal commands broadcast by speakers.  In addition to the driver’s other divided attention tasks that the driver must normally perform , police stopping a driver cause more divided attention tasks.  A driver has to react to the signals to stop, determine how and where to stop, all while still continuing to drive until a safe point to stop is reached and then braking the vehicle.

Once the driver pulls the vehicle over and stops it, the officer will make additional observations of the driver that may suggest impairment.  Examples of a police officer’s observation of a person’s demeanor/speech/appearance to show impairment to support a charge of VC 23152(a): loud/aggressive behavior; slurred speech; red/watery eyes; an odor of an alcoholic additive/beverage

Examples of a police officer’s observation of a person’s performance of the field sobriety tests to show impairment to support a charge of VC 23152(a): inability to follow instructions; repetition of instructions, failure to maintain balance, swaying, staggering, raising of one’s arms to maintain balance.

The National Highway Traffic and Safety Administration (NHTSA) instructs police at pages VI-2 and VI-3 to use their sight, hearing and smell to detect possible signs of impairment once police engage in face to face contact with a driver whom they have stopped.  Please note: all information referenced to “NHTSA” is from their February 2006 Edition, DWI Detection and Standardized Field Sobriety Testing.

I am using the language from NHTSA and DWI Detection and Standardized Field Sobriety Testing, because law enforcement is trained with this information and book.  I want you, the reader, to see what law enforcement if being told about DUI investigations, because you have more likely than not, been subjected to a DUI related investigation conducted in part based on techniques and procedures attributed to NHTSA.

Common signs of alcohol impairment per NHTSA at page V-3 include:

at .03%, slowed reactions

at .05%, increased risk taking

at .08%, impaired vision

at .10%, poor coordination.

Personal contact, or face to face observation”, as NHTSA at page VI-2 and VI-3 calls it, allows the officer to use his or her three senses of sight, hearing and smell to gather additional evidence of alcohol and/or drug impairment.

The office, per NHTSA, at page VI-3 may see the following clues that may be evidence of alcohol and/or drug impairment:

bloodshot eyes

soiled clothing

fumbling hand/fingers

alcohol containers

drug or drug paraphernalia

unusual actions

The officer may, per NHTSA at page VI-3, hear the following that may suggest alcohol and/or drug impairment:

slurred speech

admission of drinking

inconsistent responses

abusive language

unusual statements

The officer may, per NHTSA at page VI-3, detect with his or her sense of smell the following that may suggest alcohol and/or drug impairment:

alcoholic beverages


“cover up” odors like breath sprays or gum

unusual odors

Police are taught, per NHTSA, at pages VI-4 and VI-5, to create divided attention situations after they pull a driver over while the driver is still seated behind the wheel.  The techniques require the driver to do two or more things at once and involve both questioning and mind/body tasks.

NHTSA cautions that these divided attention tasks are not as reliable as the standardized field sobriety tests, but can still be “useful” to obtain evidence of impairment.

NHTSA encourages the officers at pages VI-4 and VI-5 to use certain questioning techniques.  NHTSA teaches the officer to use three kinds of questions that involve divided attention:

asking for two things simultaneously

asking interrupting or distracting questions

asking unusual questions

Have you ever wondered why the officer always asks you at the same time to produce your license and registration?  In doing so, the officer is using a divided attention technique to observe your response.  NHTSA at page VI-4 instructs the officer to watch for the following responses by the driver who

forgets to provide both documents

provides documents other than the two that the officer wants

fails to spot the license and/or registration as the driver looks for them in his/her

wallet or purse

mishandles or drops the wallet, purse, license or registration

is unable to remove the documents from the person’s wallet or purse

NHTSA at page VI-5 instructs police to interrupt you or distract you.  Asking interrupting or distracting questions forces a driver to change focus, and thus try to answer two different and competing questions.  NHTSA suggests to the officer that while the driver is responding to the request to produce his or her license or registration, the officer ask an unrelated question like, “Without looking at your watch, what time is it now?”  Possible impairment may be the driver who

does not answer the question and focuses only on producing the license

answers the question but fails to remember to continue his/her search for the license or registration after answering the question

answers the question in a “grossly inaccurate” manner

NHTSA at page VI-5 also encourages the officer to ask you “unusual questions.” NHTSA believes a sober driver would easily be able to answer them, whereas an impaired driver would not.  The alcohol would render more difficult the driver’s ability to process the question, especially when the driver does not expect that kind of a question in the context in which the driver finds himself or herself.  Such an example of an unusual question would be when asked about his or her middle name, to provide instead his or her first name.  NHTSA believes that such a response shows that the driver may be impaired, because the driver ignored the unusual question and focused on responding to the usual one.  However, the usual question, what is the driver’s first name, was not asked.

NHTSA at page VI-5 identifies two other techniques that involve divided attention that the officer may use.  The first is having the driver recite part of the alphabet.  The officer would ask the driver to recite the alphabet beginning with any other letter than “A” and stopping at any letter other than “Z.”  The driver’s attention is divided, because the driver must focus on beginning the alphabet at an unusual point and remembering where to stop his/her recitation.

A second divided attention technique at pages at VI-5 and VI-6 is to have the driver count backwards.  The driver’s attention is divided attention, because the driver must continuously concentrate on counting backwards and simultaneously remembering where to stop.  NHTSA advises police offices to never give starting and stopping points that end in a “0” o “5” because these numbers are too easy to recall.  Instead, the officer should, for example, order the driver to count backwards beginning at “63” and stopping at “47.”

Lastly, as the final point in the “face to face” phase of impairment gathering information by the officer, NHTSA at page VI-6 suggests that the officer observe the driver as he or she exits the vehicle.  Signs of impairment in exiting the vehicle may be the driver

reacting in an angry or otherwise unusual way

being unable to follow instructions

being unable to open the door

exiting the vehicle when it is in gear

climbing out of the vehicle

leaning against the vehicle to maintain balance

keeping his/her hands on the vehicle for balance

Find out how you can defend against your DUI arrest!  You should contact an experienced DUI lawyer Mark Blair for a free, informative and confidential consultation to develop your DUI defense!  Mark has represented thousands of persons who have suffered a DUI arrest.  Please call Mark Blair at (408) 295-4343, (650) 344-4343, (510) 845-4343, (415) 664-4343 (925) 935-4343 or (707) 252-4343.

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