Converted rail lines now function as bike paths, but the French seem to have done a better job at the conversion than the English, according to this report.
"The French have converted the railways into broad, hard-surfaced tracks, suitable for rollerbladers and wheelchairs as well as cyclists. They have also kept control of vegetation around the path, so that for the most part the surrounding countryside can be seen and enjoyed.
On the British side the paths are so overgrown that they resemble tunnels, providing barely a glimpse of the world outside. Mile after mile, this becomes monotonous.
Only one of the British disused railways (the Cuckoo Trail) has a hard surface - and it was being well used by wheelchair users and elderly people in mobility scooters the day I travelled down it. The others have lumpy surfaces of cinder, chippings and earth, that are barely manageable on a narrow-wheeled road bicycle."