In principal, it's fairly simple: there needs to be some way of describing each part of the train, and some way of describing each part of the platform, and some way of telling passengers which part of the train will stop at which part of the platform.
Describing trains is more or less sorted: if a description is used at all, carriages are (universally?) lettered. It's describing platforms where the problems start in that there are three options in use
- colour zones
- numbered zones
- front/rear of the train, and not forgetting
- no system at all.
I don't like front/rear as a system: it requires railway knowledge from the passenger, and is less helpful than it might be at (in particular) New Street where it is not obvious to a layperson which end of the station the train will be arriving from, and not clear if 'front' and 'rear' apply to the train as arriving or as departing.
Numbered zones are ambiguous against numbered platforms. Lettered zones are ambiguous against lettered coaches (and, I think, aren't used for that very reason). So unless we want to invent a whole new system, that leaves coloured zones.
Then the information needs to be communicated. If this is going to be passive through posters, that needs the trains to
- have consistently lettered coaches
- always be the same way round
- consistently stop in the same position
Absent any of these points, that means dynamic communication of what's happening today - which means messages on the PIS and/or the Tannoy. And that also means the relevant information being held on the system and available for communication. I don't know enough to be able to say if it is just a matter of extracting information that is already there, or whether it is yet another thing that would have to be recorded and managed.
And one last wish: let's have one common system, so that the end user only has to understand one set of railway rules, and not separate ones for every company they travel with.