The Turbos and other improvements are coming not just to the Severn Beach Line, but to a much wider 'Greater Bristol' area covering North Somerset, South Gloucestershire, Bristol, Bath & North East Somerset. Shouldn't all the rail users in those areas be contributing more too, if that is to be the reason for SVB Line increases?
Not if their fares are higher already.
Let's look at an example. NLS is 8 miles journey from Temple Meads, Avonmouth is 9 miles (less by road admittedly).
Current Fares:
Off Peak single
Nailsea: 4.40 (4.50 in peak)
Avonmouth now: 2.00 (same in peak)
Avonmouth new: 3.00
Off peak return
Nailsea: 4.50 (4.90 in peak)
Avonmouth now 3.00 (same in peak)
Avonmouth new 4.00
Weekly season
Nailsea: 23.50
Avonmouth now 9.00
Avonmouth new 15.00
With regard to seasons, the NLS weekly season gives a saving of just £1, or 4% on the daily peak cost of 4.90x5 and more than the off peak return price. Hardly the big saving you are suggesting. Whereas the Avonmouth fare currently gives a £6 saving or 40%. It will still give a saving of £5 or 25% under the new proposals.
At £9 for a weekly, the fare is 10p per mile, compared with 29.3p a mile from Nailsea. Turning that around, pax from Avonmouth pay just a third of the rate that Nailsea passengers do. And NLS is of course just an example, other stations will be similar.
So fares will still be much cheaper than other lines in the Bristol area, and yes, I do think a substantial rise is necessary, appropriate and overdue.