Yes the case of railway lines is interesting. We considered railways for the book but of course they weren't generally walked during the course of their original purpose. We even considered tracks walked by e.g. signalmen to reach places on the railway, but couldn't find anything really signficant. Now, of course, disused railway lines have been given a vital new purpose, both as inner-city pedestrian and cycle routes and for leisure walking in the country. The work of Sustrans could be a book in its own right (in fact, there probably is one!).
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