On departing St Austell and heading towards Truro, have you wondered why there is a good distance of single track, apparently for no reason at all. If my memory serves me correctly, this was single tracked because of the close proximity of mine shafts in the area. Cornwall is famous for its tin mines, which at one time, in history, supplied the majority of the worlds tin. Some of these mineshafts are under that piece of single track, and it was thought, by BR, at the time that the ground there could not take the passage of heavy trains travelling in both directions at the same time. There was always the slight possibility that there would be a mine subsidence causing the ground under the track to disappear, so single tracking that piece was their answer to the problem. Seems to have been successful. So, that’s the reason why.
It was single tracked purely as an economy measure, a bit like Swindon to Kemble or parts of the Cotswold line. Basically to save maintenance costs on a railway where for most of the day there is one train an hour or less in each direction. As the section has since been redoubled, I doubt it had much to do with subsidence...
