DC DUI Pre-Arrest Process

Before an officer can make a DUI arrest, an officer must have a basis for making a traffic stop. It does not need to be a suspicion someone is under the influence of alcohol; it can be for anything from making a rolling stop at a stop sign or a broken tail light to speeding or improper window tint. Once the stop has been made, the officer must identify an independent basis for suspecting an alcohol or substance violation. The overview below should be used for purely informational purposes. If you have questions about a traffic or DUI stop in the District of Columbia, or field sobriety tests, you should consult with a DC DUI lawyer.

The Traffic Stop

A police officer may stop a vehicle for a variety of reasons. These can include:

  • Unsafe driving
  • Exceeding the posted speed limit
  • Failing to remain in your lane
  • A broken tail light
  • Driving without headlights
  • Illegal window tints

Speeding leads to many DUI arrests because it is easily detectable: drivers may be “caught” speeding by laser, radar, or by an officer pacing a car. Additionally, driving erratically or in an “unsafe” manner can also support an officer’s suspicion that a driver is impaired. One possible way to destroy the government’s case for a DUI prosecution is to challenge the validity of the police stop. If a car is stopped illegally, anything an officer obtains during that stop will be “fruit of the poisonous tree.” This means an attorney can argue that any incriminating evidence, including the results of field sobriety tests, must be suppressed. As a result, prosecutors may drop charges or the court may dismiss a case.

Instances Where an Officer Would Make a Traffic Stop

When officers are observing a vehicle in motion, their attention may be drawn to a moving violation, an equipment violation, an expired inspection sticker, or unusual driving actions. When it comes to behaviors that are more specific however, certain indicators suggest that a driver may be impaired. As a DUI lawyer in DC can explain, however, these indicators are not foolproof and often have nothing to do with impaired driving.

The National Highway Traffic Safety Administration (NHTSA) has identified the following as the most common and reliable initial indicators that a person is driving under the influence:

  • Slowed reaction speed to stimuli
  • Impaired vision
  • Poor coordination and gross motor skills
  • Driving at least 10 mph below the speed limit
  • Following cars too closely
  • Driving with headlights off
  • Signaling inconsistent with direction of driving
  • Turning abruptly or illegally
  • Braking erratically
  • Tires riding on the center or lane marker
  • Drifting in the lane
  • Making wide turns
  • Occupying two lanes while driving
  • Weaving in a zigzag pattern
  • Driving on the wrong side of the road

Police look for these and other visual clues during a traffic stop in an attempt to provide reasonable articulable suspicion to initiate the stop.

Officers Sense Clues of Impairment During a Traffic Stop

During a traffic stop, police officers look for visual clues to validate their suspicion that a person is driving under the influence of alcohol:

  • Bloodshot eyes
  • Fumbling fingers
  • Alcohol bottles
  • Driver’s face too close to the steering wheel
  • Nervousness
  • Watery Eyes

During a traffic stop, police officers listen for the following indications of impairment:

  • Slurred speech
  • An admission of drinking
  • Abusive language
  • Unusual statements

Police officers also use their sense of smell during a traffic stop to gauge whether a driver has been drinking:

  • A lingering odor of alcoholic beverages
  • Cover-up odors, such as excessive perfume or mints

Standardized Field Sobriety Tests

When a police officer suspects that a driver may be impaired by alcohol or drugs, the officer will likely have the driver perform a series of tests to confirm that suspicion and gather evidence of the driver’s impairment.

To gauge a driver’s level of impairment, law enforcement officers may ask the driver to complete a series of psychophysical field sobriety tests. Before conducting any sobriety tests, however, officers assess a driver’s level of impairment by asking the driver to produce a license and vehicle registration. This simple request is a divided attention test because it requires the driver to perform two tasks, one mental (processing the request) and one physical (retrieving the items).

In addition to requesting multiple items simultaneously, other common divided attention tests include interrupting the driver while speaking, or asking distracting or unusual questions. Although evidence of a driver’s impairment may become obvious as an impaired driver struggles to respond to an officer’s questions promptly and appropriately, the three most significant psychophysical tests are the three Standardized Field Sobriety Tests.

The National Highway Traffic Safety Administration (NHTSA) has established the guidelines for law enforcement’s use of three Standardized Field Sobriety Tests (SFSTs): the Horizontal Gaze Nystagmus Test (HGN), the Walk-and-Turn Test (W/T), and the One Leg Stand Test (OLS). Based on NHTSA’s research, these three tests are the most accurate tests for determining driver impairment. Other tests, such as counting, reciting the alphabet, and the finger-to-nose test do not meet NHTSA’s standardization requirements; thus, these tests are used less frequently.

An important point to remember is that the officer administering the test has made an initial judgment that the driver is under the influence of some intoxicating substance. With this judgment already formed, it is more likely the officer may misread clues by expecting them to be present. The results of the SFSTs are compromised if the officer deviates from the standardized procedures, and mistakes are easily and often made. This is just one reason why it is imperative to contact an attorney immediately after submitting to a field sobriety test.

Horizontal Gaze Nystagmus

Normally, the eyes appear to move smoothly when following an object horizontally through the field of vision. Under the influence of alcohol or drugs, however, the eyes lag behind the tracking object and then jump or jerk to correct themselves. Law enforcement officers observe this involuntary, jerky eye movement, or “nystagmus,” to determine if someone has been drinking because it becomes more noticeable as a person’s blood alcohol level rises.

Indicators of Impairment

NHTSA regards the Horizontal Gaze Nystagmus (HGN) test as the most accurate of the SFSTs. Officers are trained to identify three different clues in each eye for a total of six possible clues. A person fails the test if she exhibits four or more clues.

An officer will begin the test by passing a stimulus (most often a pen) in front of the driver’s face and instructing the driver to follow it with her eyes. The officer will observe the driver’s pupils to see if they track the stimulus smoothly and equally. The officer will continue to observe the driver’s eyes through multiple passes of the stimulus, looking for “distinct and sustained” nystagmus at maximum deviation (furthest point of vision field), and the onset of nystagmus before the eyes reach a forty-five degree angle to the side. To check for vertical gaze nystagmus, the officer holds the stimulus in the center of the driver’s face and raises and lowers the stimulus while looking for nystagmus. If four or more clues of horizontal gaze nystagmus are present, the officer will conclude that the driver is under the influence of alcohol or other drugs. If the officer observes vertical gaze nystagmus, the officer will conclude that the person is seriously impaired.

The accuracy of the nystagmus test is questionable because there are many factors other than alcohol that can cause a person’s eyes to jerk or jump involuntarily. For example, looking in the direction of the spinning, flashing lights of an officer’s patrol car or rapidly moving traffic in close proximity may cause optokinetic nystagmus. Optokinetic nystagmus is caused by the eye’s attempt to focus on the distracting lights moving in and out of the driver’s field of vision; the problem is that optokinetic nystagmus looks just like HGN, resulting in a false HGN reading by the officer. Certain drugs such as seizure medication can cause nystagmus. Nystagmus may also result from severe nearsightedness, astigmatism, inner ear problems, and damage or trauma to the brain. Your DC DUI lawyer may use these inconsistencies to contest the validity of field sobriety test results.

Walk-and-Turn Test

The second Standardized Field Sobriety Test is the Walk-and-Turn (W/T) test. For the W/T test, the officer will instruct the driver to place his hands by his sides, place his left foot on a line and touch his right heel to the toe of his left foot. The officer will instruct the driver not to begin until told to do so. The officer will instruct the driver to take nine heel-to-toe steps, turn in a prescribed fashion after the ninth step, and take nine heel-to-toe steps back to the starting position.

Indicators of Impairment

NHTSA has identified eight clues of impairment that officers should look for while the driver is performing the test: (1) losing balance while the officer is explaining how to perform the test; (2) walking before the instructions are finished; (3) stopping after starting to walk; (4) breaking the heel-to-toe walk by more than half an inch; (5) stepping off the line; (6) raising arms more than six inches for balance; (7) turning improperly; or (8) taking an incorrect number of steps.

When administering the W/T test, the officer should make sure that the test is conducted on a straight line and a reasonably hard, flat, dry, non-slippery surface. The officer should also make sure the driver has enough space to take nine steps. The officer should give the driver the option to remove her shoes if the heels of the shoe are taller than two inches as such footwear can cause balance problems.

The more clues of impairment that an officer observes, the greater the chance that he will conclude the driver is intoxicated in excess of the legal limit. The government usually relies on research that has concluded that if the driver exhibits two or more clues of impairment or cannot complete the test, there is a 68% chance that the driver’s BAC in above of 0.10. If a driver exhibits four or more clues on the Horizontal Gaze Nystagmus Test and two or more clues on the W/T test, there is an 80% chance that the driver’s BAC is above 0.10.

In addition to footwear, other conditions may pose challenges for someone when performing the W/T test such as back or leg problems, inner-ear problems, fatigue, and old age. Moreover, this test presupposes that everyone performing it has the same balance and physical abilities.

One-Leg Stand

The third SFST is the One-Leg Stand (OLS) Test. The OLS test is another divided attention test that requires the driver to listen to and follow instructions to perform a physical task. Like the W/T test, the OLS test should be administered on a dry, hard, flat surface. The officer instructs the driver to stand with both arms at her sides, raise one foot approximately six inches off the ground, and count aloud “one thousand-one, one thousand-two, one thousand-three” until told to lower the foot. The officer times the subject for 30 seconds.

Indicators of Impairment

During this test, the officer watches for four clues of impairment, including swaying while balancing, using arms to balance, hopping to maintain balance, and putting the foot down. When two or more clues are present, the subject fails. Research indicates that failing the test equates to a 65% chance of a blood alcohol level over 0.10.

As with the W/T test, drivers wearing heels longer than two inches should be allowed to remove their shoes before attempting this test. The results of this test are not as reliable for drivers who are more than 50 pounds overweight, advanced in age, or bothered by back, leg, or inner-ear problems since each of these conditions are known to have an adverse effect on a person’s balance. Moreover, this test also presupposes a standard level of balance and physical condition for all subjects.


Law enforcement and courts rely upon the results of SFSTs when deciding a person was impaired while driving. These test, however, can be seriously flawed. Police officers often unintentionally deviate from the standardized manner in which they are taught to administer the Standardized Field Sobriety Tests. This is because the controlled environment of academy training does not prepare officers for the unexpected variables that effect sobriety test takers in the real world.

Additionally, during training, memorizing all the details of how to properly administer field sobriety tests is just one of many complicated subjects that officers must commit to their short-term memory. Understandably, then, some of the details are lost amid the morass of new information. Despite the fact that most officers who incorrectly administer the sobriety tests do so unintentionally, the NHTSA training manual is clear that any deviations from the standard procedures compromise the validity of the tests.

When properly administered, field sobriety tests may have some validity; however, on the streets, their use often discriminates against innocent drivers (e.g., drivers who are nervous, physically disabled, fatigued, advanced in age, etc.). The officer giving the test has already decided at the time of the test that the driver is likely intoxicated, making him more likely to misidentify innocuous behavior as signs that a person is too impaired to drive. This is especially problematic because the officer is the sole judge and interpreter of how the driver performs the tests. Given that these tests are most often voluntary, drivers should carefully consider whether to decline the SFSTs if there is a chance that the results would be an inaccurate reflection of their level of intoxication.

This information is not a substitute for the legal advice of an experienced DC DUI lawyer. If you have specific questions about facts in your case, please consult with an attorney at (202) 618-9898.