The need for construction of a new railway line arises because of one or more of the following considerations.
(a) Strategic reasons It is sometimes necessary to extend the existing railway line to a new point of strategic importance so that the defence forces can move quickly to the same areas in case of any emergency such as the threat of war.
(b) Political reasons A new line sometimes becomes necessary to serve the political needs of the country, for example, the railway line from Pathankot to Jammu.
(c) Development of backward areas Railway lines are sometimes constructed to develop backward areas. Experience has shown that once railway communication is available, backward areas develop very fast. The Assam rail link can be classified in this category.
(d) To connect new trade centres Sometimes new trade centres are connected with railway lines for the quick transportation of goods between two trade centres or from the point of production to the point of consumption.
(e) To shorten the existing rail link The existing routes between two important points may be longer than required. New railway lines are constructed on a shorter alignment in such cases. A short route is not only economical, but also helps in the faster movement of goods and passengers. The Konkan Railway is a typical example.
Doubling of existing single railway lines is also done in a few cases to cope up with the additional requirement of traffic. Recently, a large number of projects have also been under taken for converting the existing metre gauge lines into broad gauge lines in order to have a uniform gauge for the smooth flow of traffic.