Right, there's so many Trolls in the community who said they've found second Bus or something along them lines, unless they have proof don't walk into the Troll Trap.

On to the Theory, once you gain the Nav Card there's nothing you can do with it. I think there must be something to do with the Power Room. I went into Theater Mode, disabled the fog and when under the map. Underneath where that Lightning Guy spawns there's 2 or 3 massive what look like Teleporters. You must need to get into the them and it will take you somewhere out the map to another location.

Teleporting to a different location is maybe why you can't see the separate Bus Route when in Theater, there's Code and a Voice Note giving us proof there's another Bus.
Coding has been found the Zombies Files saying that it costs a certain amount to start the bus and other stuff.
Voice Note, this has also been found in the Zombies Files, it says "Navigation Card accepted, learning new Bus Route" this HAS been found in the files, type it in on YouTube if you cannot believe me.

For now I still have no idea what the table is for to read the Nav Card under the Pylon.

If you guys have anything else you want to say leave a comment below!
Also it wouldn't hurt to give some Rep :3