Concept:

There are various methods of railway alignment in mountain regions as discussed below:

Switch-back alignment:

• In the case of steep side slopes, a considerable gain in elevation is accomplished with the switch-back method of alignment.
• This method involves a reversal of direction achieved by the switch point.
• The switch point is normally located in the station yard.

Spiral alignment:

• This method is used in a narrow valley where a small bridge or viaduct has been constructed at considerable height to span the valley.
• In this case, normally a complete loop of the railway line is constructed so that the line crosses the same point again at height through a flyover or tunnel.

Zigzag alignment:

• In this method, the railway line traverses in a zigzag alignment and follows a convenient side slope which is at nearly right angles to the general direction of alignment.
• The line then turns about 180° in a horseshoe pattern to gain height.

Adaption of straight alignment for mountain regions is less preferred because it will lead to a very steep track. This will be difficult for traveling and construction. Thus for easy attainment of heights spiral, zigzag or switch-back alignments are followed.