The local users of the line wait slightly impatiently to get off at the station just up the track while the tourists run along the train shooting wildly.
It is this mix of tourists and locals that makes this line viable 30 years after Beeching should have axed it. Tamar Valley was saved by a geographical accident. The buses which were supposed to replace rail services could not get up the steep and windy roads which connected the little villages along the line with Plymouth.
The train takes 45 minutes from Plymouth to Gunnislake, on the Devon/Cornwall border, passing through a handful of villages. While many rural lines around Britain are being killed by neglect and stealth - the usual tactic is to run the statutory minimum of just one train per week - some, like Tamar Valley, are thriving thanks to the efforts of both British Rail managers and local people.
Tamar Valley has a lot going for it. There are constant views of the Tamar as it snakes towards the sea, and the little stations such as Bere Alston, where the train has to reverse out of the station, are just the sort of places where Bertie Wooster alighted for weekends at a country house. A bicycle standing unlocked, with its owner nowhere to be seen, increases the feeling that modern ills barely touch this part of Britain.
At Gunnislake, the end of the line, there is a new station, created ironically with money from Cornwall County Council's roads budget. The council wanted to allow large lorries to go along the A390 between Tavistock and Liskeard, which required the demolition of a narrow bridge next to the station, shortening the line by 100 yards.
Local residents such as Jay Kenyon, who boarded at Calstock to travel to Plymouth, live in fear that the line will be closed. 'It's just so important to our village,' she said. 'At the moment, my partner and I can cope with one car, but we would have to get another if it closed down.'
David Mather, the BR manager in charge of Tamar Valley and eight other rural lines (plus a group of much more commercial lines across South Wales and the West), promises there is no intention to close it.
He said: 'I went to a local meeting and they all expected me to tell them when the line would be closed. I told them it would last at least 50 years.'
Lines like Tamar Valley will never make money, but their losses can be dramatically reduced. 'We used to need pounds 9 subsidy for every pounds 1 we got in the fare box. Now we've reduced that to pounds 2 or pounds 3,' Mr Mather said. He also pointed to the importance of consulting local communities about matters like timetabling and seeking their help in publicising services.
Better use of rolling stock - such as taking coaches off commuter lines in summer to put them on rural lines - means that costs have been slashed.
A railway projects officer has been appointed to work on developing the lines. Special days like 'travel free if you have an umbrella' - which boosted use of one line by 10 per cent in a year, and Santa Claus specials are used to increase the number of passengers.
Mr Mather says: 'It's no good having the lines just for tourists. Local people have got to use them, but many don't even know about the service or think that there's just one train a day.'
It is a battle that can only be won slowly. When Ivybridge station, near Plymouth, opened in July, just seven commuters got on the first two trains, and one of them was a BR manager.