Some friends and I were traveling from Slovenia to Austria by train recently. It was a busy, so naturally we had reservations, and naturally, we were involved in a dispute regarding said reservations. Eventually, our seats' challengers left when the conductor told them that they were in the wrong car.
From this experience, we deduced that train reservations were inherently flawed, and spent a bit of the remaining train ride coming up with a simple, easy to implement solution to remove a bit of ambiguity from train seat reservations.
Note that the proposed solution, possibly also the problem itself, is something very European. My train experience outside of Europe is limited to Japan, and I couldn't imagine such disputes happening there.
The reservation holder must be able to identify their seat without reason for doubt.
Let's define our train as such:
By introducing an improved way of identifying seats, we can reduce reservation disputes, and help people figure out sooner that they are in the wrong carriage or train.
The Europena Vehicle Number (EVN) uniquely identifies rolling stock in Europe.
If we combine the relevant parts of the EVN with the seat number (R for reservation, usually 3 digits or less), we get a unique ID for each seat in Europe with this structure:
S S C C C C D D D R R R
Example: 85 1234 567 012
That's very verbose, and nobody is going to compare all the digits to make sure that they are in the right seat.
We can make this more readable by converting the parts identifying the carriage to base 36. Why not a higher base, such as the commonly used 64? Base 36 can be expressed without using mixed-case Latin characters, which limits potential for confusion. Now, our previous example looks like this:
E2SWSN - 012
I also added a dash to separate carriage from seat for readability.
All the passenger rail companies selling reservations "just" have to add some extra info. It should already be in their systems, so it's "only" a matter of formatting it right.
As a professional software engineer, I know that this can cause problems, but it's probably easier than switching a country from left-hand traffic to right-hand traffic.
On the hardware side, the simplest solution would be adding carriage ID stickers to every existing seat sign. If the rail company feels fancy, they could even replace the signs. If the rail company owns modern rolling stock, they can just update the displays above the seats.
A system like this probably won't be implemented, because the problem being solved isn't really one for most people. It only comes up rarely, and when it does, a conversation (maybe with the help of a conductor) resolves the matter.