THE SECOND THAT COUNTS

Manawatu Times, Volume LIV, Issue 7061, 8 November 1929, Page 12

THE SECOND THAT COUNTS

Quick Thinking And Good Brakes

SCIENTIFIC AMERICAN TESTS

How quickly can you stop your car 1 ? This is one of the apparently simple yet exceedingly complicated questions. It sounds easy—foot on the brake pedal, hand reaching for. the parking brake and trusting to good equipment. That part of it is simple, say the scientists of the Federal Bureau of Standards, who have co-operated with Dr. F. A. Moss, noted psychologist of George Washington University. The braking equipment on good oars they recognise as certain and dependable. There is no question about that. But it is here that the problem grows complicated, for there is the human element that must be taken into consideration. Human beings —unstandardised, variable, concerned with the ten thousand affairs of a complicated civilisation —are not to be trusted to the same extent as the mechanical equipment of the modern motor car. This is the scientists’ premise laid down by the investigators. The scientist of to-day is practical. With millions of motor cars on the streets and highways the exact degree of dependability exercised by their drivers grows daily more important. Four-wheel brakes, good tyres, etc., will do their full duty for us, but how about the other fellow with his uncertain mechanical appliances? If the mind works fast enough, and the muscles respond instantly when the eye calls for action, we go on our way in safety. But if in the fraction of a second the driver hesitates before using whatever equipment may be provided for him, then a fender or two may have to be “bumped out.’’ The interval between the time the need for action is observed the • time that it takes the driver to press down with his foot on the brakes is called by science the reaction time.

Dr. Moss and his colleagues attached two revolvers to the running board of a motor car. One revolver was discharged to signal the driver of the emergency. It was the call for action. The shot left a red mark on the highway. The second revolver was connected with the brakes. The exact instant the driver applied the brakes after hearing the first shot, this second gun was discharged, leaving another distinct mark. The firing of the guns, plus the speed of the car, plus the red marks on the pavement indicated the reaction time of the drivers tested. A special speedometer was iK'Cd for minute accuracy in computing the final scores. The problem, “How quickly can a driver stop?" be'came a mathematical, scientific, psychological one, with the human being as the unknown factor, “X.”

Dr, Moss used for his subjects 50 college and high school students, twelve taxicab drivers, twelve officers of the Motor Transport Corps of the United States army. All these were tested at graduated speeds. The drivers varied in their reaction scores. The grand average was slightly more than one half second. Some were as low as 0.31 of a second and others as high as 1.02 seconds. Dr. Moss believes that there are many drivers found on the streets whose reaction times are as long as 1.5 or even 2.0 seconds. This is scientific confirmation of what you say to

your self when waiting for the trues., flivver or whatnot to decide to do something and do it. Taking the average of slightly more than one half second, he calculated that “if a driver with a reaction time of such an average were travelling at the rate of 30 miles an hour, ho would go approximately 22 feet after hearing the signal before boginning to apply the brakes, whereas a driver with a reaction time of one and a half secods would go 66 feet before beginning to apply the brakes.’’ “It should be borne in mind,’’ Dr. Moss said, “that this does not represent the time required for the brakes to stop the machine, but is the time that will elapse before the driver even puts his foot on the brake. From this it will be seen that even though a machine had the finest set of brakes possible, the driver could not begin to stop it in the 50 feet usually allowed at a speed of 20 miles an hour if he happened to have a one and one half seconds reaction time.

“In no jurisdiction is there the requirement that in order to qualify to operate a motor oar an individual must be able to move his foot from the accelerator to the brake within a specified time. Yet standardising the element in this respect is fully as important as standardising the .mechanical element.’’ The tests for the future driver are thus outlined, that is if scientists and psychologists have their way about it! And they probably trill. Of the groups tested with revolvers and red marks the students varied the most. Taxicab drivers showed a general average of .41 of a second, but most of them had been driving oars for more than six years and from eight to fourteen hours a day. Experience was thus indicated as of special value. Here, say the men of science, if an individual is able to shorten his reaction time in two years from 0.70 seconds to 0.55 seconds, this would indicate that the life of the road had been of benefit. The congested traffic of the future will require mental qualifications equal to the reliability of the mechanical equipment of good motor cars, Dr. Moss and the Federal scientists believe.

Dual carburettors, as equipment for eight-cylinder oar engines, have recently c-ome into special prominence, and, compared with the single carburettor, give a gain in power in the middlespeed range between 1400 and 2800 revolutions per minute. Tests made on a number of eight-cylinder engines of both the “straight eight” and “V” types confirmed this gain, which was, ■however, unaccompanied by any-partic-ular gain in fuel economy. Carburation problems are relatively simple with the dual system. Low velocities can be used, and a nearly uniform mixture gives good results except at low speeds. Dual carburettors have not successfully replaced the single system on six-cylin-der engines because of the blow-bach of fuel spray and air charge from the mouth of the carburettor. This condition probably could be remedied by a slight change in the valve timing, but this would not be altogether satisfactory.