It's not the technology that important here but the fare structure.

There are several other metro areas using exactly the same technology
where there is no opportunity for a systematic overcharge to occur.

Could you unpack that for me please? I'm not really into these things
but ISTR being told in HK, Tokyo and Melbourne that one had to use the
card in *and* out to get the lowest fare. Does it not follow if there
is anything other than a flat fare?
--
Robin
PM may be sent to rbw0{at}hotmail{dot}com