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Scientific Basis for our Drink-Driving Laws by Greg Chester



Scientific Basis for our Drink-Driving Laws by Greg Chester

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Tabled Paper 911


Tabled Papers for 6th Assembly 1990 - 1994; Tabled Papers; ParliamentNT




Tabled by John Bailey


Made available by the Legislative Assembly of the Northern Territory under Standing Order 240. Where copyright subsists with a third party it remains with the original owner and permission may be required to reuse the material.




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MARCH 1992 CLERK PAPER TABLED C\ likely to be involved in an accident than those who had not. Furthermore, there is a logarithmic relationship in the correla tion of crash probability and the blood alcohol concentration of the driver. Chemistry and physics, for the devel opment o f simple and accurate methods to determine the concentration of alco hol in the breath and blood. As a consequence of these studies, most countries in the world have insti tuted legislation, based upon the B AC of drivers, in an attempt to reduce the inci dence of alcohol-related deaths and in juries on the road. Why 0.05? Why has the limit for driving a motor vehicle in most states o f Australia been set at 0.05 gm alcohol per 100 ml blood? This figure has not been chosen arbitrar ily; it is the result o f research using epi dem iological m ethods to identify the number of drivers driving on the road whilst under the influence of alcohol. The data are derived from two groups of drivers: those involved in a road crash; and those who have not been involved in a road crash. The technique used in this research is that o f the case-control study. The case is a road accident. As soon as possible after the accident the blood alcohol con centration of the driver is taken by the research team. This is usually done by breath analysis. The controls are derived from drivers who are not involved in a crash. These control data are collected from d riv e rs o f v eh ic le s random ly stopped at the site of the (case) crash. The research team attend the site of the crash at the same time of the day and under similar weather, light and traffic conditions as those which applied to the time of the crash. They randomly stop one or more vehicles and test the driver for alcohol. In these cases the driver is breathalysed; a simple and non-invasive technique. The null hypothesis o f this study considers that if alcohol plays no role at all in crashes, we would expect to find the same proportion of alcohol intoxi cated drivers in both of these groups. The results have firmly rejected the null hy pothesis. Drivers who have consumed alcohol are more likely to be involved in a road crash than those who have not. The results also show that the higher the b lood a lco h o l concentration of the d r iv e r , the more likely it will be that s/he will be in v o lv e d in a crash. T h ere have now been m any studies o f this na ture conducted in several countries in c lu d in g A u s tralia. The results o f all o f the stud ies are essentially the same: alcohol plays a dose-de p en d e n t ro le in road crashes. The data illustrated in Figure 1 is based on the results of four studies from North A m erica.2 From this figure, one can estim ate that the probabil ity o f being in volved in a road c ra sh w hen the BAC of the driver is0 .05g% isabout double of that ex pected with zero BAC. As the BAC increases, the in c re ase in p ro b ability of a crash increases in logar ith m ic p ro p o r tions. At a BAC o f 0.1 g%, it is seven times greater, and at 0.15g% it is about 25 times that at zero. What is frequently not recognised is just how much these results owe to the very special pharmacological properties o f alcohol. A m ong the psychoactive drugs, alcohol is unique. The unique properties of alcohol These important properties can be sum marised as follows: The rate of metabolism of alcohol is independent of the dose taken. This is because alcohol is metabolised by the liver enzyme, alcohol dehydro genase, which in all but very low 40 30 20 E_j CD O CE Q. LU r in cc 5 1 ' > I .00 .02 .04 .06 .08 .10 .12 .14 .16 .18 .20 BLOOD ALCOHOL LEVEL (per cent) Figure 1: Relative Probability of Crashing at Various Levels of Blood Alcohol Concentration doses is saturated. The individual differences between people in the rate at which alcohol is metabolised are between the relatively narrow range of 0.012 to 0.025 gm alcohol per 100 ml blood per hour. M ost 1. See for exam ple: R. N Satanen & H. Summala, Road User Behavior and Traf fic Accidents, North Holland Publishing Co., Amsterdam. 1976. 2. The data in Figure 1 is taken from Staysafe 1, Alcohol and Other Drugs and Road Safety: First Report, Parliament of New South W ales Joint Committee on Road Safety, NSW Government Printer, 1982. The Staysafe data was derived from J.L. Birrell, Drinking, Driving and You, Sun Books, Melbourne, 1974, p. 51.

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