A map showing the location of GWR troughs in the 1930s is reproduced in the book 'The Great Western Railway'. They are typically at spacings of 40 to 50 miles, but with some wide variations. There are a few instances of trough locations very close to major stopping points; for example Fox's Wood, near St Annes Park, two miles from Bristol Temple Meads; however this was installed when trains to South Wales travelled via Bath and Filton, using these troughs; after the opening of the South Wales direct route via Badminton, numerous passenger and goods trains continued to use the route and required the troughs. The lengths are also given: they vary from 524 to 620 yards (480 to 570 metres).