RSA works like this.
-
12627-12628-12658-12657-12627 and the cycle continues. Here only PM is done for 12628 at SBC. And the same rake goes as 12658 that night. If KK gets delayed, PM gets delayed and Mail gets delayed consequently. In this way, SWR has ensured that outgoing KK bound for NDLS is not affected by the arrival of incoming KK as it is 12657 which will depart as 12627 and not 12628. It is planned in such a way that as the time difference between the arrival of 12628 and departure of...
more...

12627 at SBC is very less and it is NOT possible to send 12628's rake back to NDLS as 12627 without PM. It is Mail which will get impacted due to these delays.
-
First Mail was having RSA with MAS-SBC SF( now running as MAS-MYS SF). When SWR was formed, Mail was given to SBC Divn. To run Mail separately, two rakes are required and also pitlines for PM need to be allotted. Also, since this is a short distance ONT. So, rake will lie over at the destination for a whole day. By amalgamating Mail with KK, pitlines are saved for the SBC CDO as PM will be done only for KK Express. And the need for two complete rakes for a 6 hr journey is also eliminated. In CDO's perspective, there is no legendary or train representing a state. They try to optimise the utilisation of the rakes available.