NMA DUI/DWI Fact Sheet ( PDF )
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The technological backbone of the nation’s anti-drinking and driving crusade is the Breathalyzer test. This is the process where the breath of suspected drunk drivers is tested for the presence of alcohol. The Breath alcohol content is then converted by a standardized formula to determine the Blood alcohol content, which is the actual indicator of impairment.

The whole process appears very scientific, very equitable, and very fair. The problem is that the process is not any of these things. It is not scientific nor does it rely on existing and accepted science. It is not equitable in that there is a wide variation in the results from person to person. And, it is not fair given that persons who are not realistically impaired are found “guilty” of drunk driving and persons who may be significantly impaired escape detection as drunk drivers.

Blood alcohol content can be accurately measured by a blood test. Blood alcohol content has been generally accepted as an accurate indicator of impairment. Setting aside the accepted fact that alcohol tolerance and effect varies greatly from individual to individual I want to exclude that issue to focus solely on the ability of the breathalyzer to accurately determine Blood alcohol content by measuring Breath alcohol content.

Peer reviewed and uncontested studies (LaBianca, Simpson, Thompson prove a margin of error of 50 % when comparing breathalyzer estimates of Blood alcohol content to actual Blood alcohol content! That means a breathalyzer reading of .1 % represents a Blood alcohol content level somewhere between .05 % and .15%, hardly a level of precision on which to base an irrefutable presumption of guilt!

When confronted with this proven inability of breathalyzers to accurately represent Blood alcohol content some state legislatures, in their wisdom and desire for expedience, have decided to grant Breath alcohol content the same status as Blood alcohol content as irrefutable evidence of intoxication, impairment and drunk driving. This is criminal in its error and implementation. Breath alcohol content is a legitimate measurement of only one thing, the alcohol content of the sample of air it is measuring. It is not an accurate indicator of Blood alcohol content, nor an accurate indicator of alcohol related impairment.

Breathalyzer readings should not be considered as per se evidence of Driving While Intoxicated (or impaired) unless the reading is high enough to overcome the inherent 50 % margin of error. That means a Breathalyzer reading must exceed .2 % in a state with a .1 % DWI threshold to be granted per se status (irrefutable presumption of guilt).

Breathalyzer readings above .1 % and below .2 % should be accorded prima facie status (rebuttable presumption of guilt). Breathalyzer readings below .1 % should be accorded no credibility beyond providing probable cause for a DWI arrest. In no case should breath alcohol content be considered an accurate measurement of Blood alcohol content or the degree of impairment.

The desire to eradicate the deaths, injuries and property damage associated with drunk driving does not excuse the courts or legislatures from their duty to provide just laws that are fairly administered. If standards, limits and quantities are included in these laws they should be relevant to the subject at hand, clearly delineated, and accurately measured. If there is room for substantial error there should be appropriate opportunities for the accused to address those errors in their defense. The “rush” to arrest and punish drunk drivers has badly trampled these principles.