Mumbai has trains atleast, Nagpur has almost no dedicated trains of its own, also speeding up is not a big issue. After UDN-JL was doubled, trains ran on single line TT for about 2-3 years. Only recently all trains were heavily speeded up in that section. DD-WADI has recently been electrified (doubling still pending) so don't expect speedups immediately. 1-2 saal lagega atleast