** The official reason for higher avg speed of VBs i.e. faster acceleration of trainset is a minor factor, especially for trains having limited number of stops. Faster acceleration saves substantial time if train stops at large number of stations/ every station.
** Trainsets should be introduced on priority for trains having large number of stoppages like Chhatisgarh express, Mumbai-Amritsar express etc which have stop at every 25 kms, so that their avg speed may increase a bit and they can keep pace with other trains with lesser stoppages to some extent.
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more... Above shall minimize the instances of trains overtaking and increase sectional capacity making scope for introduction of more trains.