Alcohol Tolerance and the Ability to Operate a Motor Vehicle

In most DUI cases, there are two charges:

1. Driving while intoxicated
2. Driving with an excess alcohol level in the blood -- specifically .08% (known as the "per se statute").

The prosecution normally presents a chemical test for both the per se count and as proof the defendant was intoxicated. In California, a BAC test result over .08% allows for a legal presumption of intoxication.  This presumption can be rebutted, though, by other evidence that the reading was not accurate and/or that the defendant was not under the influence.

More than once, scientific studies have verified the idea individual tolerance is different from person to person. See, for example, Sullivan, Bronstein, and Hauptman, Lack of Observable Intoxication in Humans with High Plasma Alcohol Concentrations, 32 Journal of Forensic Sciences 1160 (1987).  In the study, individuals who have had a history of abusing alcohol were hospitalized and studied after drinking large amounts of alcohol. The result – scientists discovered no relation between the BACs and the patients’ calculated level of intoxication. The conclusion the researchers came to was that because the patients had been abusing alcohol for such a long period of time, they had produced a higher tolerance. In another study, 20 patients were researched after being admitted to a detox unit in an English hospital. None of these patients showed any negative symptoms even though they had BACs above the lethal limit when they were first admitted. (See Redmond, Alcohol Blood Levels, 16 Annals of Emergency Medicine 374 (1987))

In another study conducted that same year (Maylor and Rabbit, The Effect of Alcohol on Rate of Forgetting, 91 Psychopharmacology 230 (1987)), the effect intoxication had on memory was researched. It was discovered that blood-alcohol levels often do hinder the ability to recall. However, it was also found that the correlation between physical performance and the BAC of an individual is, in fact, not that remarkable. Owing to the differences in absorption and metabolism rates, the BAC reading deduced by a breath analysis is a bad way to assess an individual’s capacity to perform.

Because of individual tolerance, the BAC of an individual is not an accurate indicator of actual intoxication, as found by research at the Alcohol Research Center at the University of Colorado. Reported from the University’s Public Information Office on December 20, 1983, results of the research indicated that defining a "drunken driver" by measuring blood alcohol levels does not give enough clues to the degree of the individual's judgment or physical response impairment.

In conclusion, blood alcohol concentrations can be determined with Breathalyzer tests, urinalysis or blood sample analysis. However, this number does not necessarily relate to legal intoxication -- that is, impairment of the individual’s mental and motor skills to the degree that he or she cannot drive safely.  

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