Ian Jelf wrote:

I *think* there's an interurban or suburban tramway somewhere in the US
that does the exact opposite of this, ie you pay at exit on inward
journeys and at entry on outward. This was done in order to
concentrate the majority of revenue on one point which was (presumably)
a large and well-equipped City Centre terminal station.

If it's a flat-fare system, which a lot of the US ones are, that makes
a bit of sense as it would mean that (assuming losses from people
fare-dodging for journeys not including the city centre were not
significant) you'd only need to maintain one set of barriers and
equipment.

Paying on exit does, however, have the disadvantage that you must get
at least a small proportion of people who only realise they don't have
appropriate means of payment after the debt has been incurred by
completion of the journey, rather than noticing when you pay beforehand
and therefore being able to address the issue before it's too late.

Neil