My understanding is that with Oyster, the system isn't capable of "refunding" the fare to less than the Clapham-Paddington fare that's charged when you touch out at Paddington (to begin the OSI).
However, at peak times, the "default" CLJ-WDT fare is the same as the "default" CLJ-PAD fare anyway, so this isn't an issue. At off-peak times the former is cheaper, so you do have a potential issue.
I'm not sure how any of this interacts with daily or weekly capping, mind.
Is the potential issue not resolvable by ringing them up, though?
In terms of off-peak fares, TfL's single fare finder gives a 'fare' and two 'alternative fares', both of which are the same and are more expensive than the 'fare'. The single fare finder describes the circumstances in which each of the alternative fares apply:
- Via Zone 1 changing between National Rail and London Underground at Victoria or Waterloo (or Blackfriars, Cannon Street, Charing Cross, London Bridge or Waterloo East)
- Via Zone 1 changing between National Rail and London Underground at Vauxhall (or Battersea Park/Battersea Power Station or Queenstown Road/Battersea Power Station)
Would you not say, therefore, that if the passenger travels via zone 1 but does not change between NR and LU at any of
- Victoria,
- Waterloo,
- Blackfriars,
- Cannon Street,
- Charing Cross,
- London Bridge,
- Waterloo East,
- Vauxhall,
- Battersea Park/Battersea Power Station or
- Queenstown Road/Battersea Power Station
then TfL is only entitled to charge the £2.10 fare?
I struggle to see how the single fare finder result for Clapham Junction to West Drayton could be read any other way? The would-be passenger is surely entitled to conclude that the existence of a list of interchange stations that are said to attract the higher fare means that the higher fare is only applicable to journeys involving a change at those stations?
While I realise doing that may mean that where a passenger passes through zone 1 but doesn't pass through any barriers, a lower fare than advertised would be charged as the system would not be able to distinguish those journeys from those that avoid zone 1, I rather think that would be less likely to erode passenger confidence in PAYG than charging a higher fare than advertised when the passenger uses the OSI at Paddington. And if somebody went from Clapham Junction to West Drayton via the OSI at Paddington, was charged the 'alternative fare' and rang up for a refund of the excess, I can't think what cogent argument TfL could make for not agreeing to refund the passenger?
Alternatively, could TfL make the higher, zone 1 fare the 'fare' and the cheaper one the 'alternative fare', and require use of the OSI at Shepherd's Bush to validate the alternative fare?