Read slowly with concentration, its too long & complicated if u don't know about routes, So i have given idea about the route first.
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TKPR & BTNG are Zonal interchange points. TKPR interchange point 'mainly' takes Load originating from/terminating at Sealdah division, whereas BTNG takes major load originating from/terminating at Barddhaman & further.
ЁЯФ╣The positive point of this TKPR-BTNG route is, it...
more... is double line. The negative point is, No Loops are available at TKPR & LLH (so once an express enters the route after a freight, it has to continue after it for several hours)...AND trains have to wait a long time at Liluah outer (for Ex.TKPR & Ex.BLY freights) & Tikiapara outer (for Ex. LLH freights),for clearance of path.
ЁЯФ╣The positive point of BTNG bypass line is, it is semi-double line with 5 loops at Bhattanagar,3 lines at Bankra,a flyover at Dankuni for Dn direction freights, (so they don't have to take T/O over busy mainline & also fits 2 goods trains),Train can also enter by taking T/O over mainline (humsafar does) and has 4-5 loops at Andul.
ЁЯФ╣Now the question is...Which would be better route for Humsafar Exp?
The answer would be the BTNG route. Because...The freights ahead of the train can be looped at any looping station to give path to the express, after providing precedence,the freight can continue journey & Humsafar would not enter the jampacked SRC HWH section, so it won't get late
ЁЯФ╣Now u can ask why TKPR-LLH bypass is not suitable. The answer is because,
SDAH div randomly sends empty BCN to SE via HWH div. HWH div has to receive randomly & then tries to send them via-Rajchandrapur-Bally-Liluah-Tikiapara. So there is always back-to-back freights in LLH-TKPR route. The freight can't be looped to give precedence to the Express once it enters this bypass line, so the Express will get horribly late.
ЁЯФ╣Again, the main purpose of this diversion is to increase punctuality of 12503. 12503 gets severely delayed b/w SRC-HWH. Further L/C at HWH & providing path to the train affects other trains regularly. So the main purpose is NOT to let the train enter SRC & further...hence they made it run via the most convenient route ADL-BTNG-DKAE.