* High speed trains give an avg speed of 200-250kmph and give approx same time as air travel for a journey upto 500kms (after adjusting to travel time to/from airport and check in and luggage receipt at the end of journey). So Mum-ST-BRC-Ahm route with high pax. density is considered best route for HST in India. Others could be Delhi-UMB-CDG/LDH-JUC-ASR/JAT, Delhi-CNB/LKO, Delhi-JP-AII/JU, Mum-Pune/Nashik/AWB-AK-NGP, Mum-MAO, MAS-SBC-MYS, MAS-ED-SA-CBE, MAS-Trichy-MDU etc
* HSTs are operating in Japan, France, Germany, Italy etc countries with chaircar coaches only and a distance upto 1000-1200kms, because these countries are small. In China about HST is doing about 2300km long journeys journeys (Similar to Delhi-Chennai/Bengaluru. In India, the distances are large somewhat like China and overnight HSTs with sleeper coaches...
more... are very much feasible.
* There can be many long distance routes like Delhi-JP-AII-ADI-BRC-ST-Mumbai 1400, Delhi-CNB-ALD-BSB-DHN/PNBE-HWH, Mumbai-Pune-SUR-SC/SBC/MAS, Delhi-AGC-GWL-JHS-BPL-NGP-WL-SC/BZA-MAS/SBC etc