The dinging bell of a tram rattling through the streets of the Indian city of Kolkata is all it takes for Deep Das to have the "happiest moment" of his day. "There were times when there were frequent buses... but I still waited for the trams," the 18-year-old student said. But while their fans hail the slow-moving transport system as the "glory" of the megacity and an integral part of how historic Kolkata grew, the 151-year-old network is under threat. IMAGES AND SOUNDBITES ARRANGED IN SEQUENCES