Just finished FMAB and felt myself wondering why the nationwide transmutation circle had railroad tracks in every underground circle?

There was some interesting discussion [here](https://anime.stackexchange.com/questions/7935/how-did-sloth-lay-rail-underground) with regards to how the tracks were even able to be laid in the first place. I mean, it seems like an alchemist would be necessary at the very least to transmute ore in the underground into iron tracks, and then as for the wood, maybe carbon trapped in the ground.

I didn't feel like any of the explanations in that thread were particularly satisfactory because from what I saw in the show, with the exception of Father, homunculi don't seem to perform alchemy.

And clearly there were no teams of people entering and exiting the tunnels to lay tracks as when Sloth completes the circle in Briggs, there is no one laying tracks as he completes the digging.

All that aside though, my real question is: **why are there tracks in the first place?** They could have just been empty tunnels, right?

Is this just an unanswered question of the show? Or have I missed something?