Here is a proper, step-by-step guide to getting Yufa splines to work.
Splines\Yufa\12cm_N_line.sli and 2_s_line.sli (road markings). Installation & Troubleshooting Tips
[Help] Looking for working download links for Yufa splines
If the download includes a Sceneryobjects\Yufa folder, also place that into OMSI 2\Sceneryobjects\ .
Thanks in advance!
You might ask: Why isn't Yufa included in DLC like "Gladbeck" or "Chicago"? The answer is licensing. Yufa assets are freeware for non-commercial use, but they cannot be redistributed inside paid DLC. Consequently, every map creator assumes you will download Yufa separately. This is why manual installation is a mandatory skill for serious OMSI 2 players.