In message , David
Cantrell writes
The failure mechanism would appear to be someone touching in, and
then touching out on a gate but failing to go through the gate. So
they are still "airside", and capable of catching a train somewhere.

This is such a fundamental fraud vector that whoever designed the
system to allow it (while penalising innocent passengers whose
platform was changed at the last minute) should be hung out to dry.
What do you suggest?
Landside validators to confirm you've left the platform.

Adding more complication and putting yet more of a burden on passengers
who already struggle to use the damned system correctly is not a useful
solution.

Although I think it could be implemented without too much of a struggle
for customers. They'd just have to know that if they abandoned a
touch-in by touching out again that they could reset themselves to their
earlier state with one simple swipe.
--
Roland Perry