Great Western Railway Instructions :: SUPERELEVATION OR "CANT."

SUPERELEVATION OR "CANT."

To be given to the Outer Rail in Curves ranging from 6 to 200 Chains Radius.

Offset (Length of Cord 66 ft.)	Radius of Curve.	Minimum “Cant.”		Maximum “Cant.”
		Outer rail to be raised.	For a maximum speed of	Outer rail to be raised.	For a maximum speed of
Inches.	Chains.	Inches.	miles per hr.	Inches.	miles per hr.
16½	6	3¾	20	6	25
10	10	3½	25	5?	30
6?	15	3?	30	4?	35
5	20	3½	35	5¾	45
4	25	2¾	35	4?	45
3¼	30	3	40	4¾	50
2¾	35	2?	40	4	50
2½	40	2¼	40	5?	60
2¼	45	2½	45	4½	60
2	50	2¼	45	5?	70
1?	60	1?	45	4?	70
1?	70	1?	45	4	70
1¼	80	1¾	50	3½	70
1?	90	1½	50	3?	70
1	100	1?	50	2¾	70
?	120	1?	50	2?	70
¾	140	1	50	2	70
?	160	?	50	1¾	70
½	200	¾	50	1?	70

The amount of “cant” to be given to a curve is governed by the speed at which trains run over it, and in no case must the raising of the outer rail in Running Lines be less than is given in the column headed “Minimum Cant,” except where necessary to meet special cases, as at switches, crossings and junctions. In curves on falling gradients where high speeds are run, the outer rail must be kept well up, while on rising gradients a lesser “cant,” but within the limits of the latter, must be given. On gradients on single lines the outer rail of curves must, as a rule, be raised to suit the speed of descending trains.

The superelevation must be gradually attained at the rate of 1 inch in each 66 feet length as the curve is approached, maintained uniformly over the whole length of the curve, and run out after passing the curve in the same way.

On reverse curves, or curves with very short pieces of straight between them, the “cant” must be made gradually on the curves commencing at the middle of the short piece of straight in the latter case.

EXPLANATION.

Stretch a cord measuring exactly a chain (66 feet) across the inner side of the curve, and measure the distance (C D) between the inner edge of the rail and the cord, as shewn in sketch below.

Look for this measurement in the column headed “Offset,” opposite to which, in the column headed “Radius of Curve,” will be found the radius of the curve in chains; and in the columns headed “Minimum Cant” or “Maximum Cant” will be found how much the outer rail is to be raised above the inner one, according to the speed of trains.

Diagram showing the above curve, offset etc.

EXAMPLE.

Suppose the distance between the inner edge of the rail and the cord at C D is found to be 2½ inches, the column headed “Radius of Curve,” shews it to have a curve of 40 chains radius; and those headed “Minimum Cant” or “Maximum Cant” will shew that the outer rail must be raised 2¼ inches higher than the inner one for a speed of 40 miles an hour, or 5? inches for a speed of 60 miles an hour.

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