MIG wrote:
Paul Corfield wrote:
On 28 May 2006 02:56:35 -0700, "MIG"
wrote:

[snip everything already written]

It's really to do with the possibility of negative balance that has
been referred to elsewhere. If you had insufficient funds entering a
gated station, but the gate opened, you'd know that you were incurring
a negative balance that you had to top up later. But at an ungated
station, you wouldn't get such a cue.
If you had insufficient funds you would not get in. If your balance was
negative on entry you would not get in.

At a validator you should get an appropriate message, red warning light
and an invalid ticket "bleep". If you then proceeded to travel you
would not have a valid entry transaction on your card.

Then again, I don't know if the former ever happens. Maybe it doesn't.
I understood that the LU and DLR systems impose a deduction on entry for
pre-pay trips and you must have sufficient funds for that transaction or
else entry is not permitted. If a validating device rejects your card it
does not create any transaction on the card. The fee on entry was
originally going to be the maximum fare but that was changed to a much
lower value - I have seen nothing to suggest this has been changed. I
would say that the publicity surrounding this part of the pre-pay
concept is practically non existent.

Or maybe the negative balance is only applied if you do bleep out
within a certain time (even then, you could be returning, having got a
paper ticket the first time).
Negative balance can only happen on exit from rail systems as this is
when a balancing transaction is made to the card to cover the cost
incurred for the trip being made - the adjustment may be zero if your
journey cost is the same fare as deducted on entry; otherwise it would
be some other value up to the total fare due.

I understand that for bus trips only a positive cash balance is required
and the full fare is deducted on entry. Obviously there is not a
graduated system of fares by distance and no exit checking so this is
the only way the bus system can work. You can therefore have 10p on
your card and make a 80p charge thus leaving your card with a negative
balance of 70p.

But maybe the whole negative balance idea is a myth. It was just that
rumours of it made me wonder if I had been assumed to have made a
journey on an occasion where I bleeped in (got warning) and then got a
paper ticket.
Negative balance is not a myth and neither is having a positive yet
insufficient value of funds for an entry transaction (on the tube or
DLR).

Any clearer (assuming I'm right!) ?

I think so, and expanding a bit: if you haven't got enough funds for
the cheapest journey you could make, you get a warning and don't start
the journey. Negative balance is only possible if, having entered the
system, you then exit somewhere that implies a journey that would have
cost more than the minimum (and more than the balance), ie negative
balance is incurred only where it's a fait accompli after the journey
and you could legitimately have got in in the first place.

Unless it's a bus, when you start and finish the journey at the same
bleep. In which case, you mustn't see a warning and hop off again, and
the driver (if it's a straight bus) won't charge you.


An interesting aside (which may confuse the matter even further!) -
although you are supposed to need enough credit to cover the shortest
possible journey, I once managed to "force" a touch-in. I was boarding
at Amersham on the first train at a weekend; the ticket office was shut
and the machine wasn't working.

Although the gates were open, I made sure to touch in anyway, but it
rejected it as the balance was too low. There wasn't anything else I
could do, so I just went to get the train anyway, hoping to sort it out
at the other end; but I saw a validator on the platform (for people
interchanging to/from Chiltern's Aylesbury services) and touched in on
that, which it accepted (and thus accruing a large negative balance at
the end of my journey).

I wonder whether it is part of the setup to allow interchange passengers
more leeway because they would otherwise have to exit through a gateline
to top up, and then enter again.

--
Dave Arquati
Imperial College, SW7
www.alwaystouchout.com - Transport projects in London