Gareth Davis wrote:


For example if only the last 10 journeys are held and the period is 24
hours then a two zone tube journey could be made on peak (£2 prepay),
followed by 10 bus journeys (that would be capped at £2.50 for a one
day bus pass), followed by another £2 tube journey. The bus journeys
would have 'pushed off' the first tube journey resulting in a £6.50
total for the day rather than a £5.30 day travelcard because the first
journey can no longer be 'seen' by the program in the gate responsible
for the capping. While I admit this is a very contrived example it
illustrates the problem well - especially if the capping period is
scaled up substantially (to say, 1 week) without increasing the
journey storage capacity on the cards. And once you increase the
amount stored on the card it takes longer to read and write back -
causing lots of '96 Seek Assistance' errors as people pull the cards
away too fast without waiting for the green light. These are not easy
(or cheep) problems to solve - which probably explains the length of
time it is taking to come up with a 100% working solution - if one is
ever found.

But how do the weekly season tickets work? Are they some sort of blanket
'I've paid' signal that last a whole week? I'd have thought the same sort
of system would work for an off-peak one day travelcard* that simply says
'I've paid, let me through' and the oyster reader says 'is it after 9:30?
yep, okay'. Capping sounds complicated, whereas a straightforward off-peak
one day travelcard itself that works in the same way as a weekly (ie, don't
need to plonk on the reader on the way in or out of the station, but
nevertheless registers as valid when the driver comes up and inspects your
ticket) sounds quite simple in concept.

* Certainly not a peak - what's the point in such a minority-use ticket -
costs too much - never ever used one, never heard of anyone else paying for
one either.
--
Ian Tindale