Champaran HumSafar Express : इन अजनबी सी राहों में, जो तू मेरा हमसफ़र हो जाये, बीत जाए पल भर में ये वक़्त, और हसीन सफ़र हो जाये. - Piyush Singh

55 km/h is the actual avg speed given to a Super Fast Class by the board.
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When the TT is designed, irrespective halts, in one side, the avg speed might increase or decrease depending on the TT ahead of the other trains too.
Similarly, with less stops, irrespective to mps in the route, some trains have good avg speed end to end....
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Where as some trains do struggle after they are allotted with pile of mountain stops.
The TT avg speed changes w.r.t to the running time of a train on a track.
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This train has many stoppages inside Kerala, in other words, even increase of stoppages do bother a train's TT n avg speed.
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Even if a foreign based loco is given, there will b no effect on the running as long as the time table is the same.