In message , at 21:32:05 on Tue, 18 Mar
2014, Richard J. remarked:
There are now posters and signs around the transport network warning
against card clash, but I think the message should have been delivered
earlier and more forcefully.

That's another message from the newspaper article - the need for such
warnings, which are quite frankly a desperate attempt to cover up a
massive technology failure.

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. At that point it's much
more likely that only one would respond. Yes, I know it doesn't
currently work like that.

If the card furthest away from the reader pad is on the edge of the
acceptable range, it may or may not be read. So you might get a card
clash (neither card accepted - try again) or you might have the nearest
card used for the journey.

Another, lower-tech, option would be to have twin pads. One for Oyster
and another for contactless credit cards.

The failure is the lack of communication for several YEARS, by both TfL
and the banks. It took me some time to realise that the frequent
mis-read of my Oyster (Freedom Pass) at Tube stations was caused by the
RFID Barclaycard in the same wallet.

That can't be the case, because there's a combined Oyster/Contactless
Barclaycard which has worked perfectly well for years as an Oyster on an
Oyster-only pad.

That was long before RFID cards had any validity on TfL services.
Neither Barclaycard nor TfL had bothered to warn me.

Clashes have been known about for years - I used to have a door-entry
rfid card which I could not keep in my regular wallet as it interfered
with the Oyster.
--
Roland Perry