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Cant regard

Letters

The suggestion by Colin Davies (NCE 23 November) that Coriolis force might influence relative rail wear of left hand and right hand curves merits examination.

Consider a train travelling at 200km/hr (v = 55.6ms -1 ) around a curve of 2,000m radius.

Acceleration force by Coriolis = 2v . sin l, where . , rotation of the earth = 7.25 x10 -5 rad. s -1 and, at latitude 55degrees, sin l = 0.82.

So Coriolis acceleration force is found to be ~6.6 x 10 -3 ms -2 .Centrifugal force on the train rounding the curve (v 2r-1 ) ~1.55ms -2 . Thus Coriolis force is less than 0.5% of centrifugal force.

The centrifugal force at this speed represents ~0.16g so that, for equal loading on each rail, equilibrium cant or. superelevation of the outer rail, would need to be ~230 mm.

There will be considerable cant deficiency, which must be rigorously controlled by regular inspection and track maintenance. If we assume cant deficiency to be at present 80mm, there may well be a case, where fast traffic much exceeds slow traffic, to reduce this figure.

An increase of cant of 10mm in this example would reduce the uneven share of loading between outer and inner rail at 200kph by more than 10% which might be significant in increasing fatigue life of the most highly stressed part of the rail head.

Alan Muir Wood, Franklands, Bere Court Road, Pangbourne, Berks RG8 8JY

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