Idea for nether rail: one continuous line: Southbridge - Serpent's Pass - spawn - Newbank, with stops at SP and spawn where you can either get out or hit a button to continue.
To just copy the mechanics of the station from my town of Hard Rock Cafe in the 1.5 LTS world:
Approaching SP or spawn on a minecart you would get stopped on a slope and see signs and a button:
View attachment 144072
If you want to actually visit the place, you just get out of the minecart and break it of course. Ignore the water escalator on the left.
If you're at SP or spawn station you'll see signs directing you to the correct track depending on where you want to go, and at the track you'll see e.g.:
View attachment 144073
It might instead say "To Serpent's Pass", etc. Note the button you can see here would have the signs above/below it as in the image above.
In terms of physical layout of the rail, I think the existing spawn-SB rail should be modified to turn towards the SP portal, look around/past it, then rejoin the old SB rail, so overall we'd have:
Code:
#### SP portal
+-oooooo-+
| |
| |
| +--+ |
| | | |
| | | |
| | | |
| | | |
: : : :
: : : :
| | | |
| | | |
+-------oooooo----+ | | | |
| | | | | |
<----+ # +---...--+ | | +-----------<
to/from # spawn | | to/from
Newbank # portal | | Southbridge
>----+ # +---...-----+ +-------------->
| |
+-------oooooo----+
Not really to scale. "o" shows where the slopes are for stopping carts. I don't actually know where to fit in this part at SP for the rail
to SB, I'd need to have a play in creative to work that out.
But overall does this sound okay?