There's a huge network of ANPR cameras, if the data can be anonymised and analysed it would give some idea of where trends in traffic flows are occurring. Then an interurban bus network can be formed around it.
At the moment, nobody actually knows where people are travelling to and from, not even agencies like National Highways. Counts of drivers are done as they drive past so can only give a good idea of traffic in that particular spot.
RE: Reversing the decline in passenger numbers