Shabdbhedi Express: गति इसकी शब्दों को भेदती है, पूरब को पूर्वांचल से जोड़ती है - Dr. Abhishek Rai

Right TN and Telangana (old AP) Express were of same class since their introduction (1976).
Today TN is just a notch above, as its priority and stops have not got much affected (2183km 11 stops) over the time , Telangana has eventually got degraded due to large number of stoppages (1676km 14 stops) given especially in the state of Telangana.
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GT...
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had been historically far superior than Dakshin Exp, the difference in speed has however been reduced after Dakshin was made SF.
Dakshin-NZM-HYB-1669kms-30:00 hrs- 55.6kmph- 44 stops-37 kms
GTrunk-NDLS-MAS-2183kms-35:40 hrs- 61.2kmph-39 stops-55 kms
Dakshin-HYB-NZM-1669kms-29:35 hrs- 56.4kmph- 44 stops-37kms
GTrunk-NDLS-MAS-2183kms-35:15 hrs- 61.9kmph-38 stops-57 kms
Detailed comparison show a wide margin between GT & Dakshin regarding avg speed, stops and priority
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Comparing the 4 trains in question on common run on Delhi-Ballarsha section

TmNadu-NDLS-BPQ-1301kms-19:00hrs- 68.5kmph- 08 stops-144.6
Telngna-NDLS-BPQ-1301kms-19:55hrs- 65.3kmph- 07 stops-162.6
G.Trunk-NDLS-BPQ-1301kms-21:15hrs- 61.2kmph- 25 stops- 50.0
Dakshin -NZM-BPQ-1293kms-22:40hrs- 57.0kmph- 33 stops- 38.0

TmNadu-BPQ-NDLS-1301kms-19:55hrs- 65.3kmph- 07 stops-162.6
Telngna-BPQ-NDLS-1301kms-20:30hrs- 63.5kmph- 09 stops-130.1
G.Trunk-BPQ-NDLS-1301kms-21:35hrs- 60.3kmph- 25 stops- 50.0
Dakshin -BPQ-NZM-1293kms-22:35hrs- 57.3kmph- 33 stops- 38.0

CONCLUSION- From above, the ranking is
(1) TN, Highest priority after premium trains like Raj/Shat/Duro/GR trains
(2) Telangana just a notch below TN in matter of spees, priority, stops
(3) GT has priority similar to TN/T'gana but hence have a little bit lower avg speed large number of stop.
(4) Dakshin is a clear loser on all counts. First 3 were SF trains since their introduction, where as dakshin was originally, just an Express train which was made SF by speeding up a little in the past.