Have just discovered this series whilst channel surfing. I rarely tune in to Channel 5 as I have no need or desire to watch Australian soaps, CSI, documentaries on Hitler or Steven Segal/Jean-Claude Van Damme films.
The episode just on, 'Australia's Outback Railway', featured a trip on 'The Ghan', the 2000 mile service across the Australia from Adelaide in the south of the country to Darwin in the north.
The previous episode 'Congo's Jungle Railway', which I'm about to watch, features a journey on the Congo-Ocean Railway in the Republic of Congo from the coast at the port (and second largest city) of Pointe Noire to the capital of Brazzaville.
The final episode in the short series, 'India's Monsoon Railway' details a trip on the Konkan railway between Mumbai and Mangalore. This is a relatively new railway, opened in 1998, built through challenging terrain that the British had steered clear of when they constructed the majority of India's railways.
The episodes are available after first broadcast on Channel 5's catch-up service, Demand 5, until December 2013:
http://www.channel5.com/shows/chris-tarrant-extreme-railways