THE EYES AND SPEED

Evening Post, Volume CXXIII, Issue CXXIII, 10 April 1937, Page 28

THE EYES AND SPEED

MAIN CAUSE OF CRASHES

LIMITATIONS OF VISION

1 ;;.The ■. danger 'of driving at a speed beybnd the. range of. onels visionIrish," but analagoiis to driving beyond the;;, limits of the '■' clear. distance ; ahead —'is; emphasised by the findings -of two Americans, Mr. 1-' J. R. Hamilton Dr.',Li*iis,.-LV Thurstone, who, in a book called; "Sale Driving," have set down optical limitations they have found to be. common, to -ail human beings, .-.individual; -variations being -so slight; as 'to be negligible.. : ■ ' ./ .

•Following two years of individual

effort* to analyse the cause of accidents, Mr. Hamilton took his findings to Dr. Thurstone, of the University of Chicago.. Dr. Thurstone enlisted the aid of a'jlr. Geldreich, who spent several months employing drivers and observers and setting up mechanisms by which tests could be made. At the end of his experimental work Mr. Geldreich reported: "The basic cause of most automobile accidents is definitely established and the human limitations in automobile driving can "be stated with considerable accuracy. The individual variations were very slight, but small as they were I have devoted as much as fifty hours to a single experiment to make assurance doubly sure." The book shows that concentration increases as -speed increases, which means that the faster the driver is going the more he must fix his attention on the direction in which he is going. As the speed increases, road tests indicated, the point of concentration moves further away. This "natural" focal distance is termed one of the two. unsuspected dangers in highway speed, as the eye keeps 'jumping ahead" to meet the emergency of speed. This is the reason, the authors say, why good drivers get into trouble before they know it. They found that at 45 miles an hour the average good driver is* focusing his eyes 1270 feet ahead; at 50 miles, 1430, feet ahead; at 60 miles, 1800 feet ahead, and- at 65. miles, 2000 feet, or about'two-fifths of a mile. "Beyond 65 miles an hour," they say, "the .eye practically points straight out 'towards infinity and the focal point is the 'distant horizon on the.road. At-60 .miles an hour, which most' good drivers - feel they can;take easily on an open road without- obstructions, the • eye is being called upon'to see accurately and in detail at'over 1800 feet while it js travelling at a rate of 88 feet per second. And, of course, it can't be done." Through a long, series of experiments the authors show that as speed increases the detail .of foreground vision iades and that even at 45 miles an ■ hour foreground vision is not clear, while above 50 miles ,an hour objects like ruts, depressions, and breaks in the pavement are seldom seen, clearly. This fading they term'one,of the,major causes of bad accidents +o-good drivers. They further show that peripheral vision, or what the eye sees from its sides, diminishes in a fixed ratio as- speed goes up. Experiments which they have thus far concluded indicate, lor example, that the eye does not merely see 10 per cent, less at fifty miles an hour than it does at forty-five but nearly 15 per cent, less, while at sixty miles vision from the sides of the eye is narrowed down almost to the channel of the road. Further experiments, made on the road and.checked in the-laboratory, reveal that the human-eye has-limi-tations and time lags in space perception, in the visual perception of movement, in reactions to multiple stimuli such as are found in crowded traffic lane driving and in night vision, which would indicate that the human organism is not geared .to the upper speed brackets of the machines it attempts to operate. The authors conclude that "a highway speed somewhere between forty and fifty miles an hour includes the brackets withm which the greatest safety is to be found."