If you are north Bihar passenger who have to go barauni, begusarai, khagaria, samastipur,Muzaffarpur side from tata side. Book your ticket up to HTZ. You would get it. Then deboard at HTZ, then autos are available for barauni at 30 rs per head, then you have many train options. If luck holds good up to kiul or brya, then you have option of bgp-mfp jansewa up to bju for eastern side and up to Mfp for western side. Don't wait for entire day to get 18181. It takes 2 hours less up to bju. You would get ticket esiely in this train.
Or if you are hajipur, sonpur chhapra bound passenger book ticket up to rjpb/ Pnbe/DNR, charge is same. Then come...
more... to Hjp via auto or bus then you have options for other sides like CPR, sv, it would take 5 hours less up to Hjp than 18181.