* Backup trains are planned for crowded SF trains which run with max. permissible load (24 coaches) and cannot be further augmented.
* On the other hand emu/passenger trains normally run with approximately 10-12 coaches only. It is better to augment them with more coaches to carry more passengers, rather than planning backup emu/passenger trains to crowded ones.
* Crowded SF trains have with very long lists running into several hundreds, which assures a minimum guaranteed patronage to justify the running of the backup train.
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On the other hand there is no guaranteed passenger patronage to backup pax train as no data of waiting passengers is available.
* I think the incidences of ticketless travel is pretty high in passenger trains as compares to SF trains, so the revenue collection is poor. The poor revenue data gives a false impression to IR that the rush in these trains is not much.
* If ticketless travel is curbed in this trains, the revenue shall get a boost and Rly may get revenue data realistically indicating the actual rush in those trains and accordingly plan to augment them with more coaches.
* IR take very less interest in running passenger trains because these trains gives very low revenue collection and very high losses to IR. That is why IR is gradually converting faster passenger trains into express trains and augmenting them with ACIII, ACII, SL coaches, in order to boost revenue collection from these trains.