MOTORDOM

Dominion, Volume 29, Issue 195, 15 May 1936, Page 15

MOTORDOM

by

Chassis

THE TECHNICAL ASPECTS OF “BLIND SPOT”

Split Seconds and a Detail of Visibility

Most motorists are familiar with the term “blind spot,’’ which denotes the partial obstruction of driving vision caused by the pillars of the windscreen. In som eof the earlier closed cars the pillars were- so wide that the risks caused by blind sirots were considerable if the driver forgot that unless he moved his head from side to side when approaching a c orner or when pedestrians were seen on the road, he might fail to observe a vehicle approaching from the side, or find himself bearing down upon a person crossing a street.

Details of the technical aspects of “blind spot” published in the “Autocar” are of great interest in that they show what should be the standard with which body-builders should conform. It is pointed out that the human eyes are approximately 24in. apart, and that “if the front pillars of a car, plus window edging, l do not exceed 2}in. in width, it is as though they were not there when looking straight into the distance past them. In fact, they cause no obstruction at all to the distant view’.”

But if they exceed that width then the extent to which the vision is restricted depends on the excess of width and the distance of the eyes from the obstructive pillar. An example given is that in which the pillar is 3in. wide and the driver’s eyes are 18in. from it. In that case it is calculated that the screening effect would be sufficient to make invisible an object 20in. wide at a distance of 20yds., and a pedestrian might be overlooked. If the pillar is 41n. across, then the width of the object which could be concealed at 20yds. distance is 60in., and, it is added, “similarly at 40yds. a 4in. screen pillar can conceal an object about 10ft. wide —-as, for example, a motor‘bus head on.” The following advice is given to drivers:'“These calculations are really rather surprising to anyone who has never thought of this point before. To those who are interested I would say,

‘Drive your car out into the country and stop it at some place where you have a clear view for a little distance on each side, and try it for yourself, unless, of course, you are one of the lucky ones who has a car with narrow screen pillars. Be careful to keep your head still while carrying out the test.’ “It should be noted that the nearer one ig to tb,e windscreen the larger is the size of the blind area if present. In this respect some of the ultramodern cars with sloping windscreens are particularly bad. Most drivers do not notice the existence of this ‘blind spot' because they seldom approach or are approached by any object in a straight line with the screen pillar. But the fact that the average driver does not notice the blind spot constitutes its chief danger, because it means that occasionally at crossroads and on curves and corners some object will be seen an instant later than otherwise it would have been observed. That might easily occur as the result of the combined movements of one’s own car and of the other object keeping the latter for a few seconds in the same relative position beyond tbe screen pillar. Also, the important point is that this is likely to happen at places where the driver is sure that be has an unobstructed view. Of course, a moment later he sees the concealed object, but we all know what a difference split seconds may make. ,‘How many ‘inexplicable’ accidents are due to this cause?”