# Proceedings Volume 10, No. 1

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 edition. Excerpt: ...6 degrees which arc, or arc liable through revision of alinement, to become limiting curves as to speed, spirals should be used whose length in feet equals not less than s'A times the speed in miles per hour calculated for an elevation of 8 in., even if necessary to increase the degree of curve in order to obtain this length. Such spirals will have a minimum offset between tangent and circular curve of 2.5 ft. (3) For all curves which are not liable to become limiting curves as to speed, spirals should be used whose length in feet, when the rail is elevated for the maximum possible speed, will be not less than 30 times the elevation in inches nor two-thirds the maximum speed in miles per hour times such elevation in inches. Degree of curve should be increased, if necessary, to obtain this length. TABLE OF MINIMUM SPIRAL LENGTHS FOR LIMITING CURVES. TABLE OF MINIMUM SPIRAL LENGTHS FOR MAXIMUM LIMITS OF SPEED FOR 8 INCHES ELEVATION. The lengths in the above tables may be taken as the minimum length, as nearly as may be determined, which will give satisfactory results under all speed conditions; longer spirals may be used when desired, but never at the expense of degree of curve, and only after careful study when cost is affected. The minimum length of spiral for any curve may be expressed by the two formulas: L =.0198 D V when V = 45 or under, and L =.00044 D V when V = 45 or over, where L = length of spiral in feet, D = degree of curve, and V = speed for existing or probable future limiting curve, calculated for 8 in. elevation. It is becoming common practice to limit elevation to 6 in. on maximum curves; the above rules, applied to this practice, would give a runoff of 1 in. in not less than 40 ft. for curves of 6 degrees and over, and...