DWI Enforcement & Alcohol Metabolism

• In typical DWI enforcement, only 1 out of 100 DWI violations leads to an arrest.
• A Fort Lauderdale study showed police officers arrested 22% of drivers with BACs between .10 and .20.

Types and Production of Alcohol

• Methyl, ethyl, and isopropyl are three different types of alcohol.
• Ethanol is intended for human consumption.
• The chemical symbol for beverage alcohol is ETOH.
• Fermentation is the natural process of beverage alcohol production.
• Distillation is used to produce high-concentration beverage alcohol.

Alcohol Absorption and Metabolism

• Women have less water content (55%) than men (68%) on average on a pound for pound basis.
• "Proof" is twice the ethanol percentage in a drink (e.g., 80 proof vodka is 40% ethanol).
• Most alcohol is absorbed into the bloodstream via the small intestine (80%).
• About 20% of alcohol diffuses through the stomach walls directly into the blood.
• The pylorus (pyloric valve) controls passage from the stomach to the lower gastrointestinal tract.
• The liver metabolizes most of the alcohol in the body.
• BAC drops at an average rate of 0.015 per hour.
• It takes the average 175-pound man 90 minutes to metabolize the alcohol in one 12-ounce can of beer.

Legal Aspects of DWI

• In a DWI case, the standard of proof is beyond a reasonable doubt.
• Implied consent laws encourage DWI arrestees to submit to chemical testing.
• In a Per Se offense, the chemical test result is presumptive evidence.
• Per Se laws make it unlawful to drive with a statutorily prohibited BAC level.

DWI Detection Overview

• DWI detection is identifying and gathering evidence to determine if a subject should be arrested for DWI.
• The three phases of DWI detection are: vehicle in motion, personal contact, and pre-arrest screening.
• During Phase One, officers observe the driver operating the vehicle.
• Phase Three may not occur if the driver is badly injured, grossly impaired, or refuses testing.
• During Phase Two, officers decide whether the driver should exit the vehicle.
• Each major decision has three outcomes: yes (do it now), wait (look for more evidence), or no (don't do it).
• Officers must determine if there is enough evidence to proceed to the next step at each phase.
• DWI evidence is largely sensory.
• Field notes are crucial because DWI evidence diminishes quickly.
• Testimony preparation begins with the initial observation.
• Reviewing field notes, organizing elements, and discussing the case with the prosecutor are all important when preparing testimony for trial.
• Organized, chronological testimony covering each phase of the DWI incident is most effective in court.

Phase One: Vehicle in Motion

• Phase One includes observing the vehicle and the driver's response to the stop signal.
• Slowed reactions, impaired judgment, impaired vision, and poor coordination are common signs of impairment.
• Alcohol impairs the ability to divide attention among tasks.
• Attempting to flee, no response, slow response, abrupt swerving, sudden stops, and striking objects are clues reinforcing DWI suspicion during the stopping sequence.

Phase Two: Personal Contact

• Phase Two involves face-to-face interviews and observations of the exit.
• The major Phase Two decision is whether there is enough suspicion to ask the suspect to exit.
• Bloodshot eyes, soiled clothing, and fumbling fingers can indicate impairment.
• Slurred speech, admissions of drinking, and inconsistent responses are audible clues of impairment.
• The smell of alcohol, marijuana, or cover-up odors can indicate impairment.
• Asking for two things simultaneously, asking interrupting questions, and asking unusual questions are divided attention techniques.
• The Count Down Technique requires drivers to count out loud 15 or more numbers in reverse.
• Leaning against the vehicle is a clue to DWI during the exit.

Phase Three: Pre-Arrest Screening

• Phase Three includes psychophysical (field sobriety) tests and preliminary breath testing (PBT).
• The major decision in Phase Three is whether to arrest the subject for DWI.
• The DWI detection process ends with the arrest decision.
• Divided attention tests require subjects to concentrate on two things at once.

Capabilities Needed for Safe Driving

• Information processing, short-term memory, judgment, decision-making, and balance are all needed to drive safely.

Walk and Turn (WAT) Test

• The WAT test has two stages: instruction and walking.
• The WAT requires a real or imaginary line and a non-slippery surface.
• Subjects must take nine heel-to-toe steps in a straight line, counting out loud.
• The WAT test can determine whether a subject's BAC is above or below 0.08, 79% of the time.
• Stepping off the line and using arms to balance are clues in the WAT test.

One Leg Stand (OLS) Test

• The OLS test has two stages: instruction and balance/counting.
• Subjects must maintain balance for 30 seconds during the balance and counting stage.
• The OLS requires subjects to keep one foot elevated for 30 seconds.
• The OLS test can determine whether a subject's BAC is above or below 0.08, 83% of the time.
• Swaying is a clue in the OLS test.

Horizontal Gaze Nystagmus (HGN) Test

• The maximum number of clues for HGN in one eye is three.
• The HGN test can determine whether a subject's BAC is above 0.08, 88% of the time.
• Onset of Nystagmus Prior to 45 Degrees is the third clue of HGN.

Preliminary Breath Test (PBT)

• The purpose of PBT is to link alcohol to observable impairment evidence.
• Residual mouth alcohol and breath contaminants can produce high PBT results.
• Cooling of the breath sample and the composition of the breath sample can produce low PBT results.

DWI Statistics and Definitions

• The average DWI violator drives intoxicated about 80 times before arrest.
• An alcohol-related crash at night is four times more likely to result in death than a non-alcohol-related crash.
• "Per Se" means illegal in and of itself.
• The "illegal per se" law makes it an offense to operate a vehicle with a statutorily prohibited BAC.
• Implied consent laws state suspected DWI drivers have given consent to chemical testing.
• A person can be convicted of DWI even if their BAC is below 0.05.
• Alcohol is the most abused drug in the United States.
• "Nystagmus" means involuntary jerking of the eyes as they gaze to the side.

Clues for Field Sobriety Tests

• Cannot keep balance while listening to the instructions, starts too soon, stops while walking, does not touch heel-to-toe, steps off line, uses arm(s) to balance, improper turn, and incorrect number of steps, are the eight clues for WAT.
• Swaying while balancing, using arm(s) to balance, hopping, and putting foot down are the four clues for OLS.
• Lack of Smooth Pursuit, Distinct and Sustained Nystagmus at Maximum Deviation, and Onset of Nystagmus Prior to 45 Degrees, are the three clues for Horizontal Gaze Nystagmus (HGN).
• 45 degrees is a key angle for determining the presence of the third HGN clue.

Field Sobriety Test Reliability (San Diego Study)

• HGN – 88%
• WAT – 79%
• OLS – 83%