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The minimum railway curve radius is the shortest allowable design radius for the centerline of railway tracks under a particular set of conditions. It has an important bearing on construction costs and operating costs and, in combination with superelevation (difference in elevation of the two rails) in the case of train tracks , determines the ...
To compensate for this, the gradient should be a little less steep the sharper the curve is; the necessary grade reduction is assumed to be given by a simple formula such as 0.04 per cent per "degree of curve", the latter being a measure of curve sharpness used in the United States. On a 10-degree curve (radius 573.7 feet) the grade would thus ...
The actual equation given in Rankine is that of a cubic curve, which is a polynomial curve of degree 3, at the time also known as a cubic parabola. In the UK, only from 1845, when legislation and land costs began to constrain the laying out of rail routes and tighter curves were necessary, were the principles beginning to be applied in practice.
The degree of curvature is inverse of radius. The larger the degree of curvature, the sharper the curve is. Expressing the curve in this way allows surveyors to use estimation and simpler tools in curve measurement. This can be done by using a 62-foot (18.90 m) string line to be a chord to connect the arc at the gauge side of the reference rail.
[1] [2] [3] A larger structure gauge would also be required This was also done in Los Angeles and in Vancouver as well as elsewhere in North America. The usually or normally limited structure gauge, and tight curves, on tram tracks will also prevent trains from using tram tracks.
The following can be used to find the versine of a given constant radius curve: [2] The Hallade method is to use the chord to continuously measure the versine in an overlapping pattern along the curve. The versine values for the perfect circular curve would have the same number. [3]
The necessary cant in a curve depends on the expected speed of the trains and the radius of curvature: the higher the speed, the greater the centrifugal force. However, the curve may use a compromise value, for example if slow-moving trains may occasionally use tracks intended for high-speed trains .
For a modern, exceptionally high-speed train at 80 m/s (290 km/h; 180 mph), the minimum radius would be about 2.5 km (1.6 mi). In practice, the minimum radius of turn is much greater than this, as contact between the wheel flanges and rail at high speed could cause significant damage to both. For very high speeds, the minimum adhesion limit ...