Hello Arijit, the rail track is right in front of SBG main station entrance and goes to the old railway station (currently serving a yard), which used to ferry trains across river Ganga and Bramputra all the way to Assam through Bangladesh in pre independence times and across Ganga uptil early 70's.
The steam loco is just a souvenir for the town, as people are not ready to part with the last symbol of SBG's golden past. And sorry the loco is not working and is totally neglected by the rail administration.