overthere 2
On Moderation
You wouldn't expect the introduction of a heavy or light rail route without there already being a substantial bus service already being present. Otherwise it would suggest there isn't the demand to sustain a rail service. Once the rail service opens you would expect the bus service to reduce or even be eliminated as the traffic switches to rail. That isn't a bad thing of itself. The hope is rail also takes a decent amount of traffic from the car. Rail appears to be much better at getting people out of cars than buses.
What was the bus service like between Okehampton - Exeter and Tweedbank/Galashiels/Stow etc - Edinburgh before the rail re-openings? because, particularly with the Scottish places I would be amazed that anybody would move to, live at or commute at these places if they did not have a car so I'm guessing the buses weren't particular frequent and mostly ran empty so saying: "Empty buses means no demand for a railway but busy buses means a POSSIBLE demand for a railway" is a poor barometer.
Because, now the railways are re-opened they are surpassing all expectations which reinforces my thoughts - that as you and a couple of other posters have pointed out - that you could offer luxury, electric buses/coaches running every ten minutes from 6am to midnight but the vast bulk of motorists will ignore them but rebuild a railway and they will flock to it.
I don't know what the bus service is like between Portishead and Bristol but it will be fascinating too see when the Portishead line is reopened what proportion of passengers come from the bus and what come from the road and if there will be a cut in/scrapped Portishead - Bristol bus services.
My guess would be far more people use the train than ever used the bus which shows railways are the only way to go if we want people out of cars.