SELECTION OF ALIGNMENT IN RAILWAY

The direction and position given to the centre line of the railway track on the ground is called the track alignment. The horizontal alignment includes the straight path, its width, deviations in width and horizontal curves. The vertical alignment of a railway track includes changes in gradients and
vertical curves.

Factor in selection of good alignment of railway : 

Obligatory or controlling points

Position, Amount and Type of Traffic

Gauge-Selection

Geometric Standards

Topography of the country

Economic Considerations

1. Obligatory or Controlling Points : 

These are the points which govern the alignment of a railway track. These points can be mainly classified into two categories –

(i) Points through which a track must pass:

          • Important town and cities

          • Major bridges and railway passes

          • Hill passes and tunnels

(ii) Points through which a track should not pass

The points through which a track alignment should not pass are the

following –

(a) Acquisition of costly level which will result in heavy compensation should be avoided.

(b) Religious places like temple, church, mosque or tomb should be avoided as they are protected by law.

(c) Areas liable to flooding (i.e., water logged areas), marshy areas, cutting in snowfall areas or such unsuitable areas of alignment should be avoided.

2. Traffic – Its Position, Nature and Amount : 

The position of traffic sources furnishes control points for general location of the alignment. The nature of traffic (passenger or goods traffic) and potential volume of traffic govern the type of construction to justify the revenues. So it is essential to estimate the growth of traffic, its position, nature and amount before aligning the track. 

3. Gauge Selection: 

 In brief, it can be said that though the increase in width of gauge increases initial cost but it also increases load carrying capacity and the speed of the trains.

4. Geometric Standards: 

An engineer should design the location of a new line considering the following Geometric elements, which would give economical combination of construction and operation costs.

5. Topography of the Country : 

If topography of country is such that the use of heavy gradients is unavoidable then in such cases the alignment of the track is made by the special ways to reduce the rate and cost of high-gradients. For alignment, the topography can be classified under the following heads –

    • Valley alignment

    • Cross-country-alignment

    • Mountain alignment

6. Economic Considerations: 

Keeping in view the above factors, the alignment should be economical also. For this purpose, different alternatives of alignment keeping in view the basic purposes should be analysed from cost point of view. 

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