why do these paths remain on RTT for many years after they cease? Avonmouth coal silo hasn’t been used by DBC for over 3 years and still shows up with flows.
They stay in the timetable as they are strategic paths - if they were to be taken out, other services (in particular passenger services) would be bid into those slots and before long would never again be available for freight use.
By retaining the paths, they are preserved within the timetable planning process to enable other, future, flows to be introduced.
Also, one (not very often used) path can allow other freight services to utilise key parts of it, enabling it to run.
Eg, getting into / out of Avonmouth to /from the main line and over key junctions, which would be in all likelyhood lost if the path were to be removed permanently.
As an aside, the A4C freight planners at Milton Keynes have to have something to play with in order to plan additional / heavily amended A4C train path requests.
They are a valuable source of pathing ability which otherwise wouldn't be there.