asdf wrote:

Eh? If they have a Z12 Travelcard and make a Z3 (or Z23) journey, the
fare is the same as the Z123 fare. So touching at Bank would make no
difference to the fare charged. If anything, it's those who are using
PAYG only (i.e. who don't have Travelcards) that would need to touch
the reader.

Regardless of the journey made, I can't see any possible circumstances
under which the system would not be able to calculate the correct fare
for holders of Z12 Travelcards travelling outside their zones via Bank
without them touching the validator there, but would be able to do so
for PAYG-only users, or for holders of Z1, Z123, etc Travelcards who
are going outside their zones.

This is possibly a way to ensure that bi-directional validators have a
reasonable way of knowing if it is an entry or exit at the station at
the end of the DLR journey.

Consider these two examples given you have a Z12 travelcard and some
PAYG value on the card.

First example, you intend to go from King's Cross to Canning Town. You
touch in at the tube gates at King's Cross, take the Northern Line,
change to DLR at Bank (without validating there) and get off at Canning
Town and touch out there. Your card has a touch-in record from KX and
you are now validating at Canning Town, it should then exit your journey
and charge a single Z3 journey from your PAYG balance.

Second example, you intend to go from King's Cross to Canary Wharf, meet
someone there and then take a DLR train from Canning Town to City
Airport. You touch in at tube gates at King's Cross, take the Northern
Line, change to DLR at Bank (without validating there) and get off at
Canary Wharf. Because you are within the zones of your travelcard you do
not touch the validator, because you do not have to. You meet a friend
there and the friend then drives you in his car to Canning Town where
you intend to take a DLR train to City Airport. Now, when you validate
at Canning Town it should be an entry but all your card has is a
touch-in from King's Cross. Should it consider this an entry or exit
then? If it would automatically consider this an exit you will get an
unresolved journey when you validate at LCY later.

Why it is chosing the first example when you validate at Bank and the
second example if you are not is however not a fully clear logic to the
passenger interchanging at Bank and wondering whether or not to validate
there.

--
Olof Lagerkvist
ICQ: 724451
Web: http://here.is/olof