What set up are you going with?

[Tartar Horde]

I think like you in any serious situation BP the roads would be chaos. The dissused railway system tends to have shorter more direct routes than the roads do, and not many people are really aware that they are out there. Plus most old railway lines have embankments means that for most of the time you will be out of sight as the track is always lower than the embankment. Another good thing about old railway lines is that there tends to be a few head of Rabbits due to the cover they find, and the ease of burrowing.
A lot of the old railway system has been paved for cycles just like BP said (as has my stretch) so the going is easy and you can cover distance quite quickly (I see them as modern Roman roads lol). Another advantage is if you have a motorbike and use these old railways you can cover some serious distance without ever having to expose yourself to cars or roads. Using my railway path (trans pennine) I could walk/ride from Hornsea on the East Coast of Yorkshire to the West coast. They are a great resource for preppers I recommend everyone check out their local networks.