Cost of Chennai first phase Metro for 54KM. is Rs.
20,000 crore. So per km =Rs.370.37
.
Estimated cost for Bullet Train for 508 KM is Rs.79,087crore.so per KM cost =155.68 crore.
.
If...
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add 20% increase during construction .
Now Total 155.68+31.13= Rs.186.81 crore
.
Final
Per KM Metro. =370.37 cr
Bullet Train /km= 186.81 cr.
.
Please verify and Reply.
.
Source Links
Chennai Metro 1st
Mumbai Ahmedabad Bullet Train

* Dear friend your question practically have many "ifs & Buts' and does not have a clearcut answer.
* Actual cost per KM vary from case to case depending on the fact that whether the track is over the ground (cheapest), Elevated (costly) or Underground (costliest). Land acquisition cost is also a big factor especially in the city area.
* Terrain make a very big difference in cost, plains are cheapest, Undulating Plateau costly, Hills/valleys are costliest (especially in case of HSTs.)
*...
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Metro is constructed in large cities which are usually located on plains/plateau and rarely on hills
* Metro is normally underground or elevated where as Bullet (HST) train is normally overground or elevated.
* Hence for different hypothetical conditions, we can say that
(1) HST on hilly track should be costlier than elevated metro
(2) Underground metro should be costlier than over ground/elevated bullet train
(3) HST on Hilly track vs. Underground Metro is a tug-of-war mainly dependent on the toughness of hilly terrain. HST in Kashmir valley shall be costlier than under ground metro, for simpler hills the HAT may be cheaper.
(4) Overground HST should be cheaper than elevated Metro
(5) Elevated HST should be slightly costlier than elevated Metro
* Original HST plan and studies/surveys were conducted for ADI-Mumbai-Pune route, but Mumbai-Pune stretch was dropped because of higher construction cost required for hilly terrain between Mumbai & Pune.