Factorio Forums

Normally a Train Stop can't be built at a curved rail. However, if you build a straight track first and place the Train Stop, then you can still put a curved rail at the Stop: The resulting setup will mostly work, except that the path finding will prefer turning right and not going straight, even if that is a long detour:
It can be argued that it is always possible to construct dysfunctional setups. However, here the result is rather obscure, will often go unnoticed and the underlying issue is hard to find. (I'm saying that I spent a lot of time yesterday trying to figure out why my trains take a long detour all around my factory.)

My guess is that for the path costs, going past a Train Stop is added for the straight rail but not for the curved one.

As far as I understand it, 2.0 will have a tighter curve radius, so it might not be possible to construct this there.

The save-game has this P-shaped rail in it, or use this BP:
Copy blueprint

Everything works as expected. Train stop only binds to a straight rail and it is seen at the end of that short rail segment where it adds the penalty of a path going though a station that is not a destination. Blocking building of a curved rail here is not simple because it could be turning left instead of right and there are no obvious collisions due to bounding boxes here while the train stop would have to disallow left turn as well.