"Ben Nunn" wrote in message ...

Capping needs to be introduced, and it needs to be smart and effective. The
£90/50 Prepay limit needs to be abolished and the 'nominate a specific
station to pick up your credit' thing must go. Also, a Non-prepay
Pay-as-you-go that bills your credit/debit card would also be far better
than having to add value to the card periodically.

Performing all the calculations required to get the 'instant' capping
to work (based on your last few journies) in the time you have your
card over the reader then to write back the refund to the card while
it is still in range is a non-trivial exercise - and is limited by the
length of the journey record kept on the card. This record needs to
hold every journey over the capping period for the calculation to be
correct.

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.

From a technical point of view it would be far easier to introduce
'credit card' style billing (which I think was announced a while back)
whereby the price calculations are made based on a whole months travel
then you get sent the bill to pay at the end of the month. In this
case the backend system does not have a limited time frame to make the
calculations (in comparison to instant capping) and also has access to
all travel events for the past month to base them on. This requires a
completely new infrastructure to be installed that prints out the
bills and collects the payments, but in reality not much different
from the kind of tried and tested billing infrastructure that any
telco has had in place for years - just with a slightly more complex
pricing plan

--
Gareth Davis