Drunk in charge
MEDICINE • JOHN ROWAN WILSON
Public interest in the new road traffic legisla- tion seems to have been concentrated dispro- portionately on breath-testing. Really the breath test is the least important aspect of the legislation, since it is out of the question for anyone to be convicted on the evidence of this test alone. It is only a device for getting a driver who smells of drink to a police station. Because it has a scientific flavour to it, it is thought rather more accept- able to the. public than the nose of a traffic cop.
There are in existence some fairly accurate breath-testing machines, but they will not be the ones used. by the police. The best known of these is the breathalyser developed by Professor Robert Borkenstein, chairman of the department of police administration at Indiana University. The breathalyser operates on the basis of the known fact that the con- centration of alcohol in exhaled air is propor- tionate to that in- the blood. The subject breathes through • a tube which leads to a measuring cylinder. The cylinder rejects the first part of the breath (since this doesn't come directly from the lungs at all but from the throat and air passages). It then takes a sample of the air from the depth of the lung which is forced through an ampoule containing potassium dichromate and sulphuric acid. The dichromate changes colour on contact with alcohol and the degree of colour change gives an estirnate of the alcohol in the blood.
This apparatus in the right hands is quick and reliable, with a possible error each way of 15 milligrams per cent. However, in the hands of the police this error has been shown
to be larger, and an error of over 15 when the legal limit is put at 80 milligrams is quite appreciable. Also the instrument costs £250. This is in contrast to the apparatus which has been chosen by the Home Office which costs no more than a few pounds. It relies on the same principle as the breathalyser and also uses potassium dichromate. But the mechanism is much cruder, giving only the roughest idea, on the basis of change of colour to green, whether theislood alcohol is materially raised.
The real bones of the Act lie in what _hap- pens at the police station. This in effect means the blood test. The proposal to offer a urine test as an alternative is the kind of absurd compromise which one has come to regard as typical of the 'laws of this country. The level which counts, from the point of view of performance, is, as everyone knows, the blood level. There is no problem or danger in taking a small specimen of blood. So why not take it? The use of urine tests is bound to lead to confusion. The figure for the urine which is supposed to be equivalent to a blood level of 80 milligrams is 107 milligrams. But, as Professor Payne of the Royal College of Surgeons has pointed out, such a precise figure is completely unreal. Whille it is true that the ayeraiei.tirine/blood alcohol ratio is about 1.33;. there,ts a great deal of individual variation. It is, therefore, quite possible for a person to be convicted on the basis of his urine alcohol level when his blood alcohol is Well below the 'critical level of 80. On the•Whole, it would seem to be sensible advice to motorist's to choose the blood test. At
least it will have the merit of accuracy.
The traditional blood alcohol test, like the breath tests, depends on changes taking place in dichromate on contact with alcohol, but can be carried out much more precisely. There are two main methods, the Kozelka & Hine and the Cavett; the K & H, as it is called, has a possible error of 8 milligrams either way, the Cavett an error of 14. For this reason, an upper limit of 80 probably means in practice that any motorist who shows below 90 will get the benefit of the doubt. A newer method, using chromatography, which is more accurate and requires less blood, will probably replace these within the next few years.
The main object of breath testing is, of course, deterrence. The loss of a driving licence for a year in these days is certainly a heavy punishment, heavier (like all forms of punishment short of imprisonment) on the poor than the rich. Its probable effectiveness in reducing road accidents is a matter of human psychology, and may well be less than most of its supporters hope. If only man were a rational animal! If this were so, he would keep constantly in mind the fact that anything over two pints of beer or two large whiskies would put him in danger of prosecution; he would then weigh the chances of arrest and punishment against the pleasure of an extra drink and shake his head firmly to the bar- man. He would also refuse the cigarette offered to him on the grounds that the penalty for smoking is by any standards infinitely nastier than losing his driving licence. But does he? Not a bit of it—he takes the chance. And, once the first furore about the matter is over, I am afraid he is likely to do the same in regard to drinking and driving.
On the more imaginative, logical driver, the new regulations will certainly have an effect. Among other things, he may see it as the last knell of that short-lived period, the romantic age of motoring, when it seemed as if modern technology had presented man with a mar- vellous new, liberating toy. At the zenith of this period, the motorist had a wonderful feel- ing of freedom. He could chuck all his stuff in the back of his car and go. He could admire the scenery as he drove, stop at country pubs and drink a bottle of wine without fear of the police by the roadside. Those days, it' is apparent now, are gone for ever. Well, they were fun while they lasted.
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