A "traffic free" route is one exclusively for cyclists and pedestrians (and in some cases horse riders) away from the road. It may either segregate cyclists from pedestrians or have them share the same space.
These may be along, for example, disused railways, river or canal banks, bridleways, parks or forest tracks. They will generally be free from motor traffic, although some will provide access to premises.
It is usually simpler to build paths away from roads as there is much less regulation of what can be done. The landowner will need to grant their consent, but the guidance is straightforward to use.