Abstract
EVERY driver of a motor-car who desires to pass another car going in the same direction has to consider the problem of whether it is possible or not. Apart from the question of whether there is another car coming round the bend of the road in the opposite direction, he has to consider whether there is sufficient clear space ahead. According to a Science Service message, Dr. H. C. Dickinson, of the U.S. Bureau of Standards, has completed tests to find out how much clear space is necessary. Assuming a speed limit of 45 miles an hour and that cars travelling 50 miles an hour are tolerated, he finds that a distance of 900 ft. is required for safe clearance. The time required to pass on a level road depends only on their relative speed of five miles an hour, and is nearly six seconds. If the vehicle ahead is moving at 20 miles an hour the distance required is 650 ft., 200 ft. being required for the actual passing and 450 ft. being the necessary allowance for a car approaching at 50 miles an hour. The Highway Research Board of the U.S. National Research Council points out that, considering the number of roads in the country where clear stretches of 900 ft. are rare, there is often a serious risk when passing another car at high speed. In mountainous country, winding and hilly roads would come under this category. Dr. Dickinson's figures apply to a car passing only one car ahead; when long lines of cars ‘pile up’ on the road, greater distances are required for safe passing.
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Safe Passing Speeds for Motor-Cars. Nature 135, 465 (1935). https://doi.org/10.1038/135465a0
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DOI: https://doi.org/10.1038/135465a0