I think Bonckers Johnson came up with an idea for cyclepaths above London railway lines. Back to reality, though, I'm not sure I would want to spend too many long periods of time cycling alongside a continuous fence. That said, a path I use quite often runs along a railway line between Millwall football ground and Bermondsey in SE London, and it's flat, smooth and pretty straight but it's not long enough to irritate and has enough greenery to give a sense of space. After being overtaken by a pair of cargo bikes travelling with surprising speed, it now sets me thinking whether railway paths could become inter-town light freight routes for bikes. There's no shortage of parcel delivery trade from online orders and a few fewer vans clogging up the roads might make it an attractive proposition for more than just cyclists and the NHS.