In message , at 14:52:30 on Wed, 19 Mar
2014, John Levine remarked:
I'm not sure I'd describe it as a *technology* failure. The passenger
has presented a set of cards to the reader, two of which have validity
for the journey. What do you expect to happen in those circumstances?

A properly designed system would instruct the cards to back-off for a
pseudo random period, then interrogate again.

I still don't understand how that tells it which of the two valid
cards to use.

If it got an answer from both (with a suitable separation), it could
decide to use the season ticket rather than the PAYG. Doesn't have to
take just the first one, especially just after it had detected a clash.
--
Roland Perry