On May 3, 1:24 am, James Farrar wrote:
On 2 May 2007 13:25:17 -0700, MIG wrote:





On May 2, 7:05 pm, James Farrar wrote:
On Wed, 02 May 2007 18:38:56 +0100, Paul Corfield

wrote:
And *as* you are a genius I am sure you'll be able to work out what a
zig zag is ;-)

Zig-zag is three uses (in-out-in or out-in-out or purchase-in-out) in
quick succession, right?

What use would that be to anyone? I mean, what scam would be pulled
by that means?

When I go through the barriers at Charing Cross platforms 1 - 4, just
miss my train and have to head for platform 6 for the next one, I've
never understood why the gates won't let me out. What scam is being
prevented by it?

If zig-zag is allowed, it's tantamount to allowing passback.

Example: Passengers A and B are travelling together. B has a valid
ticket, A does not. B goes through the "out" gate using the ticket,
then puts the ticket back through an "in" gate, then passing the
ticket to A who uses it to exit. Allowing out-in-out (or in-out-in,
the logic runs exactly the same) is tantamount to allowing out-out (or
in-in) in quick succession, i.e. passback.

Example: Passenger A (who has travelled by rail from long distance) is
meeing friend B (who has arrived on foot) at a gated station. A
travels without a ticket, knowing that if the gate is closed, B can
buy the cheapest single ticket from the machine, use it in an "in"
gate and then pass it to A to use it to exit. Elimination of
purchase-in-out is necessary to prevent this


My Charing Cross example involves a travelcard. If I was meeting
someone who had travelled without a ticket, I could just pass it over
the exit gate to them, far less ostentatiously than by backing out of
the entry gate and passing it to them with someone trying to enter
behind me.

If there were no restrictions, people would just pass the ticket back,
so there would be nothing to be gained by putting the ticket through
an extra time.

Given that there are restrictions that prevent any kind of successive
passes at the same gateline, there is still nothing to be gained by
passing the ticket through an extra time, and no need to program
against it, because it's already ruled out by simpler restrictions.

I must be missing something.