Does it really start with the first drink? Impairment & DUI – Pennsylvania

While many have a general rule that if they drink, they don’t drive some still want to know how much is too much—legally.

beerThere is no easy answer to this question because everyone is different. My research in this area indicates that a variety of factors influence impairment but like anything else, the experts do provide general guidelines for alcohol consumption and the diminution of motor skills.  The easy answer is that any consumption of alcohol will slow your reaction time/motor skills.  They say that impairment starts with the first drink and they are right but my intent here is to get you think before you drink.

Our frequent readers understand that a DUI charge is composed of 3 elements: (1) Control; (2) Impairment; (3) BAC. This short article is focused on Impairment and BAC elements of a DUI. BAC is the percent of alcohol in a person’s blood stream. For example, a BAC of .10 means that a person’s blood contains one part alcohol for every thousand parts of blood. The level of your BAC is based on a number of factors which include:

  • The number of drinks consumed
  • The amount of time in which the drinks are consumed
  • Your body weight
  • Your sex
  • Food consumed

Pennsylvania defines alcohol impairment as “the diminution or enfeeblement” of the ability to exercise judgment, deliberation, or reaction to changing circumstances and conditions. This definition, however, describes a condition that may not exactly equate to being “drunk.” Remember the prosecution doesn’t have to prove that you were drunk but just impaired to the point where you couldn’t safely operate a car. They can prove this through a chemical test (Blood or Breathalyzer) or the officer’s testimony regarding his or her observations of you prior to your arrest. The severity of DUI charge is based on your impairment and prior DUI convictions. The level of your impairment is based on your Blood Alcohol Content (BAC).

While everyone’s body metabolizes alcohol at pretty much the same rate, people have different tolerance levels for alcohol based on their frequency of their consumption and the factors stated above.

Blood Alcohol Level (BAC)/Drink Matrix

 One (1) drink =

  • (1) 12 fl oz beer
  • (1) 5 fl oz glass of wine
  • (1) 1.5 fl oz shot of hard liquor 
Weight Number of Drinks
1 2 3 4 5 6 7 8 9
100 0.032 0.065 0.097 .0129 .0162 0.194 0.226 0.258 0.291
120 0.027 0.054 0.081 0.108 0.135 0.161 0.188 0.215 0.242
140 0.023 0.046 0.069 0.092 0.115 0.138 0.161 0.184 0.207
160 0.020 0.040 0.060 0.080 0.101 0.121 0.141 0.161 0.181
180 0.018 0.036 0.054 0.072 0.090 0.108 0.126 0.144 0.162
200 0.016 0.032 0.048 0.064 0.080 0.097 0.113 0.129 0.145
220 0.015 0.029 0.044 0.058 0.073 0.088 0.102 0.117 0.131
240 0.014 0.027 0.040 0.053 0.067 0.081 0.095 0.108 0.121

This table is provided as a reference and it should not be relied upon to determine whether you are capable of operating a motor vehicle. Always keep in mind that there are a number of variables that can influence whether you are legally qualified to drive.


Blood Alcohol Concentration (BAC) & Motor Skills 

BAC Typical Effects Predictable Effects on Driving
.02% •    Some loss of judgment


•    Relaxation

•    Slight body warmth

•    Altered mood

•    Decline in visual functions (rapid tracking of a moving target)


•    Decline in ability to perform two tasks at the same time (divided attention)

.05% •    Exaggerated behavior


•    May have loss of small-muscle control (e.g., focusing your eyes)

•    Impaired judgment

•    Usually good feeling

•    Lowered alertness

•    Release of inhibition


•    Reduced coordination


•    Reduced ability to track moving objects

•    Difficulty steering

•    Reduced response to emergency driving situations

.08% •    Muscle coordination becomes poor (e.g., balance, speech, vision, reaction time, and hearing)


•    Harder to detect danger

•    Judgment, self-control, reasoning, and memory are impaired


•    Concentration


•    Short-term memory loss

•    Speed control

•    Reduced information processing capability (e.g., signal detection, visual search)

•    Impaired perception

.10% •    Clear deterioration of reaction time and control


•    Slurred speech, poor coordination, and slowed thinking


•    Reduced ability to maintain lane position and brake appropriately
.15% •    Far less muscle control than normal


•    Vomiting may occur

•    Major loss of balance


•    Substantial impairment in vehicle control, attention to driving task, and in necessary visual and auditory information processing

*This information has been gathered from a variety of sources including the National Highway Traffic Safety Administration, the National Institute on Alcohol Abuse and Alcoholism, the American Medical Association, the National Commission Against Drunk Driving