"Paul Corfield" wrote

I believe, but am not 100% certain, that TfL introduced a rule
concerning "doughnut or polo mint" fraud. In other words people do not
have Zone 1 on their Travelcard but have some of the outer zones. I
believe the system does a secondary check to see if the origin /
destination pair for the journey (which may both be within the zonal
validity of the card) can *only* be achieved by travelling via Zone 1.
If that is the case then a PAYG transaction will be created to charge
for Zone 1 travel.

Clearly it becomes very complex when you have orbital routes that allow
legitimate travel on the TfL farescale that avoids Zone 1. TfL have
clearly decided to allocate particular journeys to zone 1 or non zone 1
fares. In your example your ticket included Zone 1 so the secondary
check for a Z1 PAYG charge was never initiated. As both origin and
destination were within the zones you'd bought then there is no need to
do anything to trigger a PAYG additional charge.

Now that Oyster has been extended to London Overground there aren't many
journeys between Z2-Z6 starting and end points that can't be made by a route
avoiding Z1, and avoiding out-of-station interchanges where touching out and
in would be necessary, even if the route might be very convoluted - St
John's Wood to Whitechapel via Finchley Road, Rayners Lane, Earl's Court,
Kensington Olympia, Willesden Junction, Gospel Oak, and Barking. On PAYG
time outs would no doubt come into effect, and being charged the obvious
Z2-Z1 fare would not be unreasonable, but I can see issues if the passenger
held a Z2-Z5 season ticket on Oyster.

The issues with tweaking the system to cope fairly with the myriad of
possible journeys when Oyster is extended to the whole London rail network
seem to be incredibly complex, especially when LO starts running on the East
London Line, giving even more orbital possibilities, and interchanges which
don't involve a gateline.

Peter