World's Busiest Railway 2015

Dan Snow, Anita Rani, Robert Llewellyn and John Sergeant are in India, exploring the world's busiest railway. From their base at the Chhatrapati Shivaji Terminus in Mumbai they reveal the science, systems and staff responsible for keeping this supersized transport system running to schedule. In this opening episode, Dan, Anita and Robert try commuting Mumbai-style, tackling 'super dense crush load' on the world's busiest commuter trains. With as many as 14 people crushed into a square metre, these trains are more than twice as crammed as the most crowded UK trains. Passengers hang from the sides of trains and cross the tracks, so they're in for quite a ride. John Sergeant heads to Darjeeling's steam-powered hill railway and reveals the historical connection between tea and trains. And our cameras are on board with the astonishing dabba wallahs - a crack team of couriers who deliver 200,000 home-cooked lunches to offices all over Mumbai.

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 thee million km 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 the 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.

Dan Snow, Anita Rani, Robert Llewellyn and John Sergeant go behind the scenes to reveal the hidden areas of the Chhatrapati Shivaji Terminus station unseen by commuters. Robert visits a city-sized repair facility where, every 18 months, train carriages are given their version of an MOT. He tries his hand at repairing seats and discovers that carriages are still painted by hand. Our cameras are on board with one of the train drivers - known as motormen - and are given privileged access to the lounge where they gather before going on duty. Anita heads onto the roads of Mumbai to see if commuting by road is any easier than by rail. But with an average speed of just 9 kmph, she discovers that progress is slow and hazardous by car. We're in the station control room when a train with a suspected fire on board threatens to bring evening rush hour to a halt, and we reveal the secret station workers who only come out at night. John Sergeant visits two rural stations that still operate historical systems for train control and discovers how a silver ball can keep passengers safe.

In this final episode, Dan Snow, Anita Rani, Robert Llewellyn and John Sergeant consider the challenges faced by the Chhatrapati Shivaji Terminus in Mumbai and ask what the future holds. Nine people a day die on Mumbai's railway lines. Anita tackles the railway's head of safety on the measures they're taking to reduce this fatality rate. Dan meets two eye witnesses to 2008's terror attacks that claimed the lives of 52 people at the station. He also takes a ride on Mumbai's newly built Metro to consider what the future could hold for the city's 5.5 million rail commuters. John Sergeant is in the Western Ghats, one of India's biggest mountain ranges, revealing the heavy human cost of building the line that connects Mumbai to the south and east of India. Robert fulfills a childhood dream and becomes a train driver for a day and Anita tries her hand at station announcing.