Alcohol and Driving
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Alcohol is absorbed into the blood at a rate that varies according to several factors, but disappears at a rate that is constant for any individual, varying between 5 c.c. and 20 c.c. per hour. The relationship between the level of alcohol in the blood and urine is constant, but the level is not an index of the amount consumed, as individuals vary. Legislation penalising driving with a particular level of alcohol in the blood adopts critical levels that vary from 150 to 50 milligrammes per cent, in different countries. Breath analysing machines have an optimum error of 20-25%, so are therefore only useful for screening. For these reasons Dr. Gadd does not favour legislation based on analysis results, but considers that a fair result can best be obtained by a combination of analysis, medical examination and the evidence of eye-witnesses.