ABSTRACT
The contours of the territory to be crossed by a railway are obviously decisive as to its average gradient but they are also the background to fixing the maximum permissible gradient within the limits of tractive and braking adhesion. The lower the difference between average gradient and maximum gradient the greater is the practicable train load and the lesser are the deviations from constant-speed running. The minimum curvature to be used also determines the differences between the line speed limit and local speed restrictions. Long curves of small radius on heavy gradients may involve derailment hazards for very long and heavy trains, arising from braking or tractive effort surges along the train. Both maximum gradient and minimum curvature have a large effect on the earthworks cost of constructing a railway and, because of this, the ideal of constant-speed running is often subject to heavy qualification. This is particularly the case in mountainous country.
