I placed parallel diagonal tracks without space in between and with curves on at least one side.
There are no switches, all the tracks are connected in the most trivial way.
Placing a train on either of the tracks causes signals in both directions to be blocked.
However trains can pass through in both directions at the same time without any trouble (if the
signales are removed).
Straight parallel diagonal tracks without a curve don't do this, nor do horizontal/vertical
parallel tracks with or without curves:
No Problem
I can not find any reason for this behaviour.According to the wiki page there was once a bug (0.8.8) where trains would collide in this
scenario, but that is long past.
The wiki also recommends not to lay tracks directly beside each other because “… it's
currently a big problem to switch from one track to the other parallel track, if there is no
space between them: The curves doesn't enable it!” However there is no mention of
this actually having any functional ramifications, it simply states that it might be
strategically better to leave a gap.
Well, I think that huge gap is an ugly waste of space and I feel like it should be entirely
possible to build a railway system where tracks are layed right beside each other. However
the current behaviour of signals makes that virtually impossible.
So after all this I'd consider this is a bug. If I have overlooked something, please enlighten me.
Edit: I've created another screenshot with a more realistic scenario where this comes into play:
Example