Baad mein hi hui hogi but year nahi pata. Haa 1860s mein Howrah to Delhi route via SBG loop hokar bana tha. Tabhi usko main line bolte th. 1870s mein Jhajha hokar bana toh usko Chord bolte. But baad mein Jhajha hokar traffic badha toh usko Main Line bolne lage aur original main line ko SBG loop.