How are the suffixes of railway platforms determined? [closed]

In the UK, the suffix is chosen arbitrarily. Sometimes "a" and "b" refer to different parts of the same platform, or sometimes they refer to completely different platforms! (See Stratford for perhaps one of the worst examples of platform numbering; 10 and 10a are on different islands!).

Sometimes trains "double dock" infrequently enough that no specific suffix is used, and announcements are made that the coaches "at the front" of the platform is the one you want (at a terminus station), or (for example) "furthest from the steps". Other platforms use abbreviated compass directions (I can't think of any examples right now but I could have sworn there are a few). Other times, as I said, it's pretty arbitrary when and how suffixes are applied. At stations where the platforms are most often operationally separate they can even get separate numbers for the same platform face!

On some lines the numbers (as opposed to the suffixes) tend to start at "1" for the platform on the far "up" side (usually towards London), but other lines apply different schemes.

In the United Kingdom at some larger railway station platforms are split into sections.

It was introduced to enable multiple trains to use the platform at the same time.

Depending on the station the platform may have a letter suffix (such as Birmingham New Street station) or may actually be split numerically (Bristol Temple Meads has platforms that are identified with two numbers. Eg 3 at one end, 4 at the other) the designations are so that people then get on the correct train.

Historically trains were much longer in the uk. 12 or 14 carriages long. But many trains in the UK today are much shorter, so this enables better usage.

In addition it's worth noting that some of the U.K. Operating companies also have colour zones on the stations they use (this seems to be diminishing but is worth mentioning) These were introduced so you can identify the section of the platform to wait for your correct carriage. (I.e. Carriages A and B will be ajacenent to the red zone)

To answer the question. In the UK it seems to be allocated arbitrarily.

Well. I think this answer is rather broad, not being country specific, but here goes what I can say from Austria (and AFAICT Germany does the same or similar):

The suffixes in the platform numbers are to segregate the platforms into "numbered" segments (A - D) so that you know where to stand yourself for a certain train.

E.g. A regional two-coach train might be labelled to stop at platform Xa (or Xd) so you know it will stop at the very start or end of a platform.

I find it more commonly used for long-distance trains that span a whole platform (section A - D fully): Announcements will, e.g. state "Intercity from X to Y arriving on platform 7. 1st class and restaurant car is in section B, ..."

The sections are also labelled on the coach plans on the platforms, so you have an easier time locating the right spot to wait if you have a seat reservation.