Scrolling through reddit and found a funny post:
https://www.reddit.com/r/Factoriohno/comments/1qr0niq/theres_gotta_be_an_easier_way_to_turn_trains/
(https://i.imgur.com/oQwujp1.png)
https://i.imgur.com/oQwujp1.png
It's about how to turn a train around, but it's not the most efficient way - it's a silly joke.
But stuff like that would be fun to deal with in Simutrans.
I mean, I think it's better that trains do turn themselves around since a tile is also 1km¹.... but still, this would be fun to model as well :)
Essentially a back-feeding turning heptagram. I'm not aware of any in real life, but turning pentagrams do exist. There's one in Carbonia (Sardegna, Italy; no longer used) and in Mals (Trentino, Italy). Triangles a.k.a. wyes are more common. I expect this heptagram will be even more compact than a pentagram, but there comes a point where a turntable is the cheaper solution.
In this case the train alternates between doing 45 degree turns, bypassing the exact centre, and straights, going through the exact centre, giving a very complex centrepiece. But if 45 degree turns are acceptable, better make that 36 degree symmetrical turns and turn (!) it into an ordinary turning pentagram.