"John Rowland" wrote in message
...

The obvious solution seems to be individual doors which check that there
is
a platform adjacent before opening. The basic idea seems very easy to
implement, although a foolproof system which could never mistake the sides
of a bridge for a platform might be harder to implement, but in
combination
with driver control it should be safe enough.

Something along the lines of a transponder at the start of each platform
which is detected by each door and enables the doors on the appropriate
side, and another one at the end of each platform which disables each door.
Other interlocking means that doors cannot actually open until the train has
stopped, and failsafe precautions could cancel the enabling if the train
hasn't stopped within, say, one minute of passing the transponder. Some
complications for platforms on reversible lines, but I can't help thinking
that something like this has the potential for being more reliable than the
GPS technology (Can GPS identify which line the train is on if adjoining
platforms are different lengths?)
Peter