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.