ECR website states the following regarding this bridge. Looks like they will create an alternative trunk line connecting Gorakhpur to Katihar.
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In the year 1887, a meter gauge rail link between Nirmali and Bhaptiahi (Saraigarh) was provided by the Bengal North West Railway. Due to severe Ino-Nepal earthquake in 1934 this rail link washed away in heavy flood owing to meandering nature of river Kosi, no attempt was made to restore this link for a long period.
The...
more... Kosi Rail Bridge project included in the budget in the year 2003-04 at an estimated cost of Rs. 323 Crore. After the construction of Kosi Rail Bridge, the distance between Nirmali and Saraigarh will get reduced to 20.5 KM from present 299 KM. It will provide an alternative BG route of length 610 km between Gorakhpur and Katihar against the existing route of 505 KMvia Chapra and Barauni, which at present is a highly saturated corridor.This project gained exceptional significance as the East West Corridor from Muzaffarpur to Purnia (NH 57) of NHAI shares the same location for crossing River. The bridge is 1780m long with 39 spans.