RailFanning is an art-form; RailFans are the paints - Ayush Kumar Singh

I mean to say that they are autonomous organizations under the control of the Railways. Basically they are like a parallel business segment of Indian railways.
The whole operations of Indian railways, design and construction of rolling stock and equipment, track construction, catering services etc are all parallel independent ventures of Indian railways. A good analogy is something like the TATA group or the Reliance group of industries. Both of them have many separate businesses ranging from IT services to house-hold goods manufacturing. On a particular project, TCS may provide support to Tata motors or some other subsidiary of the Tata group, but at the same time, TCS is an independent body and also does...
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projects for companies outside the TATA group. This is exactly the mode of operations in IR.
The IRCON group handles railway construction projects for India and other countries as well, while IRCTC handles catering for corporate offices in addition to catering for the Indian railways. Similarly the various coach factories and Locomotive workshops also cater to other customers while providing their services to IR. All these are subsidiaries of the Indian railways, wholly owned by the Ministry. It is a very good way for our railways to generate revenue from sources other than tickets and freight charges. It is beneficial for the general public in the end.