Whereas roads can negotiate steeper gradients railways have a limit. This is also necessitated by the length of a train, which cannot tolerate steeper gradients. This is why the Himalayan or other high mountains are mostly out of bounds for railways. The railways reaching the southern brow of the Himalaya, e.g., Siliguri-Darjeeling or Kalka-Simla railway were built when motor transport was not so well developed. The influence of geomorphology is seen in the structure, and operation of these ‘baby’ narrow-gauge railways.
Seven Hedin describes Kalka-Simla railway thus: “The little railway climbs up the steep flanks in the boldest curves, descends the slope into deep and narrow ravines, passes along steep mountain spurs, where the train seems as though it would plunge into space from the extreme point; then the train crosses bridges which groan and tremble under its weight, enters pitchdark tunnels, and again enters into blinding sunshines……There are 102 tunnels on the route”.
Darjeeling railway too is a marvelous example of adjustment to geomorphology. The train follows a tract of marvelous engineering feats. “On steeper sections the overworked engine is assisted by a fireman who sits on its fender scattering sand on the rails. The train with its black and white passenger coaches” takes some 6 hours from Siliguri to Darjeeling (a distance of 80 km).
The Mettupalaiyam-Ootacamund meter-gauge railway, the passenger trains taking about 5 hours to cover a distance of 46 km, is another example of an exercise in adjusting railway engineering to geomorphology.
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It could be said as a generalization about geomorphic permissibility of terrain for roads and railways that roads first show the way. Subsequently with economic need, financial feasibility and geomorphic permissibility the road alignment with certain modifications may be adopted by a railway at a later date. Roughly, speaking roads and railways are similar in pattern, i.e., alignment and density because of similar geomorphic requirements.
A railway map of India clearly brings out the geomorphic control on railway pattern. Geomorphology generally forbids railways from entering the Himalaya. The relatively stupendous and steep Western Ghats are generally railless except the geomorphic gaps formed by (i) Thai Ghat, (ii) Bhor Ghat and (iii) Pal Ghat, which carry the railway respectively from Bombay towards (i) Northern India and Calcutta; (ii) to Madras via Pune and from (iii) Madras to Kerala. The Satpura and Shillong horsts flanked by steep scarps on all sides are so far railless.