And commuter demand includes re-opening closed lines and especially re-opening stations. By way of an example, a number of stations have been opened or re-opened in South Glamorgan, using an existing line but adding greatly to its potential. In effect, it has created a new rail route, while using a line that was already there.
If you think about, there are very few parts of England and Wales (Scotland to a slightly lesser extent) that did not have rail coverage at the height of the 1920s usage, or similarly extensive bus coverage from the 1930s - 1960s. So any "new" public transport route is likely to simply be a permutation of an "old" one anyway (the white elephant of HS2 being an exception, obviously).
Yes, I agree there are instances where there is commuter demand for improved links. But that will only ever serve a very specific transport corridor, and it will simply not be a viable option for anyone outside easy access to that transport corridor. Public transport between major urban hubs doesn't need to be a problem, because it has the potential to be more attractive than the car (again, assuming that homes and workplaces are accessible easily from either end).
Not sure what you're getting at with the new vs old routes thing?
