Methods Used By Law Enforcement to Detect DUI / DWI

The majority of Driving While Under the Influence (DUI) and Driving While Impaired (DWI) charges begin when the driver commits a traffic related offense, such as speeding, failure to obey a traffic control device, negligent driving or reckless driving. This provides law enforcement the right to stop the driver. Once this occurs, the officer is trained to look for specific signs of alcohol consumption.

Another way that law enforcement can stop drivers is by the use of roadside checkpoints. This method provides law enforcement with immediate means to check motorists’ Drivers’ Licenses, including restricted licenses issued to offenders, vehicle registrations, vehicle equipment for safety, and vehicle identification numbers. Drivers who are not in compliance may be issued citations or defective equipment repair orders and may have their vehicles removed from the roads for safety reasons.

DWI sobriety checkpoints are also included in these safety checks. This allows law enforcement to detect whether a driver is under the influence or impaired by alcohol. When conducting DWI sobriety checkpoints, law enforcement officers are prohibited from randomly stopping vehicles. They must comply with the United States Supreme Court decision of Delaware v. Prouse, which states that law enforcement may either stop every vehicle, so that each driver has an equal chance of being stopped, or may stop every tenth or every twentieth vehicle (a predetermined number), so that the officer does not exercise individual discretion in deciding which vehicle to stop, and so that all vehicles have an equal chance of being stopped.

Furthermore, the location selected for the check must be safe for both the police and the public. Therefore, the site selected must have adequate visibility for approaching motorists, ample space to park both the police officer’s vehicle and the drivers’ vehicle, there must be warning devices on the police vehicle, warning signs along the road to notify motorists in advance, and the officers must be in full uniform with reflectorized equipment. The requirement for high visibility is good for the drivers because this allows drivers to see the checkpoint in advance and to decide whether to proceed through the checkpoint or not.

The legality of these checkpoints has been challenged in the courts on the grounds that they violate the Fourth Amendment, which prohibits illegal searches and seizures. In 1990, the United States Supreme Court upheld the constitutionality of checkpoints in the case of Michigan Department of State Police v. Sitz, and decided that they are legal when conducted in a manner minimally intrusive on the rights of the traveling public. The Supreme Court ruled that the Fourth Amendment does not forbid the initial stop and brief detention, without individualized suspicion, of all motorists passing through a highway checkpoint established to detect and deter drunk driving, which are conducted in conformity with operational guidelines, site selection, and publicity.

The National Highway Traffic Safety Administration (NHTSA) and the IACP Highway Safety Advisory Committee have published operational guidelines that police administrators should consider in order to ensure that sobriety checkpoints are legal, effective, and safe. These guidelines state that the sites should be preselected by management based on statistics, and there should be special warning devices, visible police authority, chemical testing logistics, contingency planning, effective detection and investigation techniques, operational briefings, comprehensive public information and public education efforts, and post-incident critiques based on data collection and evaluation.

Some checkpoints have Breath Alcohol Test Mobiles “BAT Mobiles” stationed on-site, which are motor homes outfitted with breath testing equipment and serve as mobile police stations. Some states use roving DUI patrols and saturation patrols in areas targeted for high incidences of DUI arrests or DUI related accidents.

During a sobriety checkpoint stop, the officer must determine that there is articulable suspicion of DUI in order to proceed with an arrest. To determine this, the officer may request that the driver provide a Preliminary Breath Test (PBT) by using a Preliminary Breath Testing instrument. This is a portable instrument, which detects Blood Alcohol Concentration (BAC). The driver blows for several seconds into this portable device through a tube and the device provides an instantaneous determination of Blood Alcohol Concentration (BAC). If the device detects the presence of alcohol or controlled substances and the driver appears impaired, the officer will seek to administer to the driver another series of tests called Standardized Field Sobriety Tests (SFSTs). If these tests are performed unsatisfactorily, the officer will place the driver under arrest, to be transported to a breath alcohol testing site where the driver will be asked to take a Breathalyzer Test.

The results of a Preliminary Breath Test (PBT) are not admissible in court as evidence of DUI/DWI because they are inaccurate and unreliable. They serve to provide law enforcement with additional objective information to establish probable cause for arrest and for further chemical testing. They also help to detect persons who may be suffering from an illness or injury such as diabetes or a head injury who are in need of medical treatment.

There are generally three types of Preliminary Breath Tests (PBTs):

a) Electro-Chemical PBTs - Alcohol in a person’s breath is absorbed into a fuel cell where it is oxidized, producing electrical current. The higher the alcohol content of the breath, the greater the current output of the fuel cell. The instrument measures the current produced and determines the breath alcohol concentration (BAC), and the BAC conversion is displayed as a number, such as .08.;

b) Semi-Conductor PBTs - Alcohol in the person’s breath increases the electrical output of the semi-conductor. By measuring the voltage output, the breath alcohol concentration (BAC) can be determined and the BAC conversion is displayed as a number, such as .08; and

c) Disposable Chemical PBTs - As the driver exhales through a tube in the device, which contains a measured amount of chemical that is reactive with alcohol, the alcohol contained in the breath reacts with the chemical contained within. The greater the breath alcohol content, the greater the chemical reaction.

As stated above, DUI laws are also enforced by the use of Standardized Field Sobriety Tests (SFSTs), developed from research sponsored by the National Highway Traffic Safety Administration (NHTSA). The tests are used to obtain validated indicators of impairment and to establish probable cause for arrest. They are administered and measured by law enforcement systematically and evaluated in a standardized manner according to the responses of the driver. NHTSA also developed a training program for police officers to detect DUI suspects, describe their behavior, and present effective court testimony.

The three (3) Standardized Field Sobriety Tests (SFSTs) are: The Horizontal Gaze Nystagmus Test (HGN); The Walk-and-Turn Test (WAT); and The One-Leg Stand Test (OLS), and are explained below:

a) The Horizontal Gaze Nystagmus Test (HGN) - Nystagmus is an involuntary jerking of the eyeball which occurs naturally as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral (near the outer edges of the retina) angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. A person impaired by alcohol may also have difficulty following a moving object smoothly with the eyes. This is known as smooth tracking. The Horizontal Gaze Nystagmus (HGN) test measures the physiological and automatic reaction to central nervous system depressants, such as alcohol.

During the HGN test, the officer moves an object, such as a pen or a small flashlight, horizontally in front of the suspect’s eyes and observes the eyes as the suspect’s eyes follow the object. The officer is trained to look for three (3) “clues” or indicators of impairment in the right eye and in the left eye. The three (3) clues are: 1) if the eye cannot follow a moving object smoothly; 2) if Nystagmus (jerking) is distinct when the eye is at maximum deviation; and 3) if the angle of onset of Nystagmus (jerking) is within 45 degrees of center. In summary, the jerking of the eye is measured in three different ways. The first technique is to look for a lack of “smooth pursuit” of an object that is placed in the suspect’s field of vision. The second method is to determine whether the Nystagmus becomes more “distinct” when the eye is moved to a lateral extreme. The third method is to measure the angle of onset of the Nystagmus. By measuring the angle at which Nystagmus begins, an officer is supposed to be able to estimate the person’s blood alcohol content (BAC).

This test is scored by determining if, between both the left and the right eye, four (4) or more of the above-stated three clues were present (there is the possibility of six (6) clues since the three (3) clues are counted for each of the two (2) eyes). If so, the suspect likely has a BAC of 0.08 or more. Although NHTSA has determined that this test provides proper classification of approximately 88% of suspects tested, it is important to know that HGN may also occur from non-alcoholic sources, such as from medications used to treat seizures, inhalants used for asthma, nicotine, caffeine, barbiturates and other depressants, as well as other sources.

Unfortunately, law enforcement officers and the finder of fact in your case, the Judge or Jury, place a high degree of reliability on this test. Therefore, it is important to have competent defense counsel explain the unreliability of the HGN test to the fact finder in your case.
b) The Walk-and-Turn Test (WAT) - The Walk-and-Turn Test is a divided attention test that requires a person to listen and to follow instructions while performing simple physical movements. Impaired persons have difficulty with tasks requiring their attention to be divided between simple mental and physical exercises. In order to perform this test, the officer must first ask the suspect if they have any medical problems or disabilities, which would impact on their ability to safely execute this test.

In the Walk-and-Turn test, the suspect is told by the law enforcement officer to stand in position while being instructed. Once instructed to begin the test, the suspect is to take nine steps, heel-to-toe, along a straight line. After taking the steps, the suspect must turn on one foot and return in the same manner in the opposite direction. The officer is trained to look for eight (8) “clues” or indicators of impairment. The eight (8) clues are: 1) if the suspect cannot keep balance while listening to the instructions; 2) the suspect begins before the instructions are finished; 3) the suspect stops while walking to regain balance; 4) the suspect does not touch heel-to-toe; 5) the suspect steps off of the line; 6) the suspect uses their arms to balance; 7) the suspect makes an improper turn; and the suspect takes an incorrect number of steps.

In practice, the officer must demonstrate the test first. If the suspect does not understand how to perform the test, the officer must explain the parts that are not understood again. In summary, this test requires the suspect to stand on a line with one foot in front of the other foot, heel to toe, while the officer is explaining the test. The officer instructs the suspect to walk nine (9) steps on the line, while looking at their feet and while counting out loud. Then the suspect must complete a four (4) step turn and then walk back nine (9) steps, heel to toe. The suspect is penalized for not staying on the line, for not walking heel to toe, for using their arms for balance, for performing an incomplete or incorrect turn, and for swaying back and forth. A suspect who steps off of the line is allowed to resume to their position before having stepped off of the line.

This test is scored by counting the number of clues observed. Only one (1) clue is counted for each type of violation, even if it occurs more than once (i.e. steps off of the line). If a suspect gets two (2) or more clues, the test is deemed to have been performed unsatisfactorily. NHTSA has determined that 79% of people who scored two (2) or more clues while performing this test will have a BAC of 0.08 or more.

c) The One-Leg Stand Test (OLS) - The One-Leg Stand Test is also a divided attention test requiring a person to listen and to follow instructions while performing simple physical movements. Impaired persons have difficulty with tasks requiring their attention to be divided between simple mental and physical exercises.

In order to perform this test, the officer must first ask the suspect if they have any medical problems or disabilities, which would impact on their ability to safely execute this test. In practice, the officer must demonstrate the test first. If the suspect does not understand how to perform the test, the officer must explain the parts that are not understood again.

In the One-Leg Stand test, the suspect is instructed to stand with one foot approximately six inches off of the ground and to count out loud by thousands (one thousand-one, one thousand-two, etc.) until told to put the foot down, while the officer times the suspect for thirty (30) seconds. The officer looks for four (4) “clues” or indicators of impairment during this test. The four (4) clues are: 1) the suspect sways while balancing; 2) the suspect uses their arms to balance; 3) the suspect hops to maintain balance; and 4) the suspect put the foot down before told to do so.

This test is scored by counting the number of clues observed. Only one (1) clue is counted for each type of violation, even if it occurs more than once (i.e. put the foot down). If two (2) or more of the above-stated four (4) clues were observed, the result will be that the test was performed unsatisfactorily.

NHTSA research indicates that 83% of suspects who exhibit two (2) or more clues in the performance of this test will have a BAC of 0.08 of more.

As stated above, if the Standardized Field Sobriety Tests (SFSTs) are performed unsatisfactorily, the officer will place the driver under arrest, to be transported to a breath alcohol testing site where the driver will be asked to take a Breathalyzer Test.

The Breathalyzer Test is an alcohol breath test, which is the most often test used by law enforcement to obtain evidence in drunk driving cases. It tests the amount of alcohol present in the alveolar (pertaining to the tiny air sacs of the lungs) air. Alcohol in a person’s blood diffuses across the semi-permeable (can be penetrated) membrane of the capillaries into the air of the lung. The instrument used to take the breath sample uses a fuel cell sensor to determine breath alcohol concentration (BAC).

There are many factors, which can influence the accuracy and the results of a Breathalyzer Test, which can result in excluding the test result from the criminal Trial. They include the presence of mouth alcohol, acetone, certain compounds, and radio frequency interference. These factors are explained below.

Mouth alcohol or residual alcohol in the mouth can contaminate a breath sample and may be present from a breath freshener containing alcohol, mouthwash, a belch, dentures, other artificial teeth, or braces capturing alcohol from a last drink.

Acetone is a compound, which we produce during metabolism, and is contained in our blood in small traces. However, diabetics and persons of Asian decent, may have higher acetone levels, which can interfere with the testing instrument.

Exposure to compounds used in paints, varnishes, rubber cement, aviation fuel and other high-octane fuels, insecticides, dyes, explosives, detergents, solvents for gums and lacquers, such as toluene, benzene, ethyl acetate, methyl ethyl ketone, and xylene, may also interfere with the breath test. These compounds may be present in a person’s bloodstream in sufficient concentration to be present in the breath and therefore, in the breath sample.

Lastly, radio frequency interference, such as from the officer’s radio, may also interfere with the instrument’s alcohol detection, if the officer is standing too close to the person providing the breath sample during the test.

It is important that a valid breath alcohol test is properly performed. If the results of a breath test have been compromised, it is critical that proper testing procedure be followed and that the test be re-administered to ensure a valid test.

Call me at 410-446-6644 or complete the Free Attorney Consultation box on this page to discuss your case at no charge and to fully protect your interests.