REACTIONS AND ROAD SAFETY
By SURGEON REAR-ADMIRAL CHARLES M. BEADNELL
ONE of the . chief causes of road accidents is sluggish reaction time on the part of certain drivers of motor vehicles. The expression " reaction time " is used here, not in its strict physiological sense where it is restricted to brain and spinal-cord operations, but to cover the entire interval between the impact of a stimulus—the light—or sound- waves from another car, a cyclist, pedestrian, or dog, &c.— on the eye or ear of the driver, and his or her response by activating and co-ordinating the muscles concerned in hand and foot movements so as to cope with the new situation thus suddenly introduced.
In the complex nervous arc involved in this process many momentous changes have to be effected in the shortest possible time, in fact, as " quick as thought." To mention but a few, the mechanical stimulus of the light or sound has first to be converted into a wave motion through highly- specialised living matter, a " nervous impulse " as it is termed. This then travels towards the brain along a specific nerve route and, arriving at the sensorium or grey-matter centre, evokes in it consciousness of the significance of the outside state of affairs which initiated the nerve-impulse. This sensing centre must then call up the correct executive or motor centre and, in conjunction with it, organise despatches along other specific, but now outwardly directed, nerve routes, of impulses destined to implement the appropriate hand and foot muscles whereby steering-wheel, brakes, horn, &c., are put into action.
At first blush it might be thought that all this would involve a very appreciable interval, but, as a matter of fact, the normal reaction period in a warm-blooded animal, such as is man, to a flash of light is only about the 4*o° second, while to that of a sudden sound'it is even less, 18aboo second. The former takes a little longer because, although the lengths of the two paths from eye and ear to brain are practically the same, more nerve-junctions are interposed in the former which the impulse has to " jump." Had birds, with their feverish," highly-heated blood, and more excitable and alert nervous system, evolved an intelligence parallel with that of human beings they would assuredly have made better motor drivers by virtue of the enhanced rapidity of reaction to environmental stimuli which such attributes confer. Conversely, cold-blooded reptiles, though imbued with the mental capacity of an Einstein, would have made more dangerous drivers than public enemy No. 1 on the roads today.
In this age of high-speed, hand-and-foot-controlled traffic, where we tacitly accept as inevitable the annual slaughtering in Great Britain alone of some 7,000 human beings, to say nothing of the maiming of another 90,000, it is just as well that man does possess this fairly quick reaction time. The indispensability of his rapidity of action becomes obvious when we remember that in the case of a car travelling at 5o miles an hour the rate of approach to a stationary object straight ahead is 73.3 feet per second, while the rate of approach—and this is a point often over- looked—between two cars travelling towards one another at this speed is twice this amount, that is, too miles an hour or 146.6 feet—close on 50 yards—per second. Fortunate is it, then, that in the healthy, normal, human being the speed with which the messages from the brain course down- ward to hand and foot with the purpose of manipulating the steering wheel and applying the brakes is about 38o feet per second, that is, well over two and a half times faster than the speed of approach between two 50-mile-an-hour cars.
There are many factors that lengthen the normal reaction time, but especially must be mentioned old age, fatigue, sleepiness and alcohol. A comparatively small quantity of the last, the amount in a cocktail, for instance, may appre- ciably slow down the rate of travel of the impulses threading the nervous route between the eye and the foot or hand. It has been experimentally demonstrated that the immediate - effect of a small dose of alcohol is, as in the case of the drug benzedrine, slightly to shorten the reaction period ; after a few minutes, however, the brain exhibits a decided slowing down in its operations. This applies to all sorts of tests, such as responding to the sudden appearance of a flag, reading aloud, doing " sums in the head," adding up columns of figures, and so on.
Perhaps the most convincing results of all have been obtained from experiments carried out with the setting up of type. The work of compositors demands great rapidity of thought and accuracy of muscle response, and the trials were made on four expert type-setters who had volunteered for the purpose, the number of letters being noted that they set up : (a) after partaking of a small amount of alcohol ; (b) after taking none. Out of these it was found that the alcohol had no appreciable effect one way or the other on one man, but in the case of the others that the work accomplished was markedly below their average ; one compositor, for example, setting up 2,212 letters when his expectation was 2,554, a deficit of 312 letters. Throughout the tests the men believed they were doing much better work, whereas the reverse was the truth. Just the same kind of impairment of nerve-muscle by alcohol is shown in lower animals. Dogs exhibiting similar activities, alertness and skill had been taught to retrieve tennis balls thrown along the floor of a gymnasium. They were let loose, two at a time, immediately after the ball was thrown, one of the animals having been given for some days small doses of alcohol with its food, the other none. Out of 1,40o throws the teetotal dogs retrieved 922 balls, the alcoholics only 478. Incidentally one might mention here that a reaction time test would afford valuable evidence in cases where a person is charged with driving a car while under the influence of drink.
Out of 361,000 driving licences issued in London in the year ending November 30th last, 19,803 were endorsed, and of these 1,821 were on account of bad driving. Now, it is more than probable that the majority of the delinquents were cases of delayed reaction time. It is admittedly impossible to protect the public from the class of driver who is possessed of a normally acting nervous mechanism, but every now and again throws it out of gear by avoidable causes. One can only appeal to his better feelings or, where this fails, have recourse to the arm of the law. But there are not a few men and women, more especially those of phlegmatic temperament, who are constitutionally organised in such manner that, even at their best, their reaction time is so far below that of normal individuals that they make potentially dangerous drivers. So long as things run smoothly these people get along fairly well but, given a crisis, their " nerves fail," there is a crash, with results disastrous to themselves and, it may be, others.
Does it not follow, then, that a part of the examination tests for prospective drivers should be the recording of their normal reaction-times ? Those below a certain standard— based on results afforded by expert drivers—should be defi- nitely refused driving licences. The apparatus for carrying out the requisite tests need not be elaborate. The examiner, by pressing a key, would complete an electric circuit which would start the registration of fractions of a second by a chronograph. At the same instant a signal would appear, on seeing which, the candidate, by pressing another key, would break the circuit and so arrest the time-registration. To introduce an atmosphere of reality the signal could take the form of a visual message thrown on a screen- " turn left," " apply brakes," " sound horn," &c., the " driver " reacting accordingly. In any case, by thus placing the test on a scientific basis, the " personal equation " of the examiner would be eliminated and many of the com- plaints of unfair treatment on the part of the examinee would be done away with. There could be no appeal against a system whereby the learner-driver had self-endorsed his or her incompetency to drive a motor vehicle on our modern congested roads.
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