RailFanning is a gift you give yourself. - Varun

By having dedicated elevated semi HSR tracks (MPS : 160kmph) along specific stretches like Arakkonam to Jolarpettai and Chengalpattu to Virudhachalam there can be decent savings in runtime of ~1hr in routes connecting important cities with Chennai. Assuming cost/km of such tracks is 100cr this would cost ~30K cr.
But such stretches should be taken up first which can later be expanded to cover entire mainlines !!

---