On Mon, 15 Aug 2005, Andrew Smith wrote:

Anybody heard of any plans for Weekly capping ?

Nope.

Presumably it would have to operate at a database level rather than from
the data held on the card,

Why?

I keep finding I do more travel than expected, and I'm paying way more
than I should do ... but I put off getting weekly/monthly travelcards in
the hope that I won't need to travel ...

Same here. Weekly, monthly and annual capping would indeed be extremely
useful.

It is potentially very complicated, though - unlike with daily capping,
there are no fixed boundaries between weeks, so deciding which days to
cover with a ticket could be tricky. For example, say you do the following
travelling:

sun - spend the day going round Z1
mon - stay at home
tue - spend the day going round Z1
wed - spend the day going round Z1
thu - spend the day going round Z1
fri - spend the day going round Z1
sat - spend the day going round Z1
sun - spend the day going round Z1
mon - spend the day going round Z1

Daily capping would charge you for a Z1 1DTC (6.00 UKP) each day you used
the tube. A simple implementation of weekly capping would kick in once
your spend crossed 18.50 UKP, which would be some time on thursday
morning, replacing your three 1DTCs and one single with a 7DTC. That 7DTC
would cover you for friday and saturday too; you'd then end up with 1DTCs
for sunday - monday.

However, if you'd actually been buying tickets, you would probably have
bought a 1DTC on sunday, then a 7DTC to cover tuesday to monday. The naive
capping has charged you 6.00 more than you needed to pay!

Is this a problem? Personally, i think so - for capping to replace
pre-buying of period tickets, it has to guarantee to never be more
expensive, otherwise people won't trust it. Some may feel that as long as
the system is transparent and predictable, it doesn't matter if it's not
always perfectly cost-efficient - if it's going to shaft you, you'll know,
and you can buy a ticket upfront to defeat it.

If you do want a perfect system, then the complexity of the system
increases dramatically - i'm not at all certain, but my gut feeling is
that the problem of figuring out the optimal combination of tickets to
cover arbitrary travel patterns is what computer scientists call
'NP-hard', which is their way of saying 'bloody hard'!

tom

--
It sounds very much like a rock group consisting of a drum machine and a
few 56k modems. -- Jon