Now I experience a bit of stuttering on all routes, but it's a whole lot worse on the San Bernandino Line. I wonder, is it something to do with my machine, or is there something wrong with the way the route was built? My machine is a i7-9700 CPU, 16GB RAM and a GeForce RTX2060 Super, running 4K but only at 30-40 FPS, which is on the low side, but I'm fine with. But it's not the FPS I have a problem with, once every few moments I'm getting a stutter or lag spike which sometimes takes a few seconds. It's a lot more frequent on the San Bernandino Line though.
Unfortunately, some amount of stuttering is normal, but is greatly reduced after a full run of the route. However, it will not be fully eliminated. You can find more information here: How Do I Optimise My PC for the Best Performance? Also, you may be pushing your graphics card too hard, causing it to run into a memory capacity/bandwidth issues, which could also cause stuttering. To avoid this, you will need to reduce your graphical settings, resolution, and set a sensible frame rate cap (i.e 60fps).
