Correct. PDY already have a weekly train to NDLS.
Grand Trunk could stay in Chennai. If really extension is needed, the best extension would be to make it go to Amritsar with extra rake cause MAS do not have proper connectivity with Amritsar. Train can leave MAS at 23:30 PM to arrive NDLS at 10:00 AM and arrive ASR at 18:30 PM ; Then goes to SM
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Train can leave ASR at 09:00 AM to arrive NDLS at 17:00 PM to arrive MAS at 04:40 AM the third day and can go to PM from morning 04:00 to night 23:00 PM - In that case it would be a possible profit for sure as MAS dont have dedicated train to ASR