In the case of very steep gradients, much steeper than 3%, it becomes difficult for a locomotive to pull the train load and hence is possible for the train slide down or slip back along the down grade.
The rack railway system consists of three rails, i.e., one extra toothed rail in the middle in addition to two normal rails. The locomotive also has a toothed pinion wheel whose teeth fit into the grooves of the central toothed rail. This locking arrangement helps to haul the train load and does not let the locomotive slip back. There are various such systems existing in the Indian Railways, such as the Fell system, Abt system, Riggenbach system, and Marsh system, each with its own characteristics.
With the help of this rack and pinion system, it is possible to move trains even on very steep gradients such as 1 in 5.
The alignment of a railway line is extremely important as subsequent costs of construction and operation depend heavily on it. The basic requirements and factors affecting alignment have been discussed in this chapter. The various types of engineering surveys required to mark the alignment of a railway line are described in the next chapter.
1. State and discuss briefly the factors that control the alignment of a railway track.
2. In the process of selecting a suitable alignment for a railway line, what factors and parameters are kept in view? What analysis is done to assess the economic viability of the alignment?
3. Describe in brief the basic requirements of a good alignment. What are the factors that control the alignment of a railway line?
4. What do you understand by mountain railways? Describe in brief the various types of alignments used for mountain railways.
5. Write short notes on the following.
(i) Spiral method
(ii) Zigzag method
(iii) Rack railway