World's Busiest Railway 2015 1of4 BBC

Dan Snow, Anita Rani, and Robert Llewellyn examine the role the Chhatrapati Shivaji Terminus in Mumbai plays in long-distance travel across India. The country's rail passengers travel three million kms every day - that's the distance to the moon and back, four times.

Anita joins passengers on a long-distance sleeper across India, to discover who's travelling, what they pay for their tickets and what conditions are like on board.

The station team have just six hours to service trains after every journey. With trains measuring more than half-a-kilometre in length this is a gargantuan task. Robert joins the team to watch this turnaround in action.

Dan gets his hands dirty with the behind-the-scenes support teams who process more than 25,000 dirty sheets a day and ensure that everyone on board is fed and watered.

And we go on board one of India's poshest tourist trains, where you can travel like a maharaja at a cost of £600 per night.