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.

I suppose, but that still doesn't help in the many cases where there
is no clear reason to prefer one card over another. It seems a poor
use of funds to redo the gates when it will only help sometimes.

Like I said, people will get wallets that more or less solve the
problem.

--
Regards,
John Levine, , Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. http://jl.ly