Hi, I noticed some issues with this mod so I came up with some fixes to help me learn modding. If you're interested here are before/after screenshots:
https://imgur.com/a/m3gwapH

The first thing was the sharp edge of the dark coal ballast on the light vanilla ballast. The ground_texture folder was missing so I "restored" it and now the dark coal ballast blends naturally into the dirt/grass.

Next there were light vanilla parts showing up in curved track. The coal rail and sleeper .mdl files were still pointing to the vanilla .mtl files so I re-aimed them at the coal rail and sleeper .mtl files.

Two things I haven't figured out yet, tho not as noticeable... The high-speed version is missing even though one is shown in the Workshop screenshot. The high-speed config .lua file seems to be missing, as is the UI icon. The other is a LOD popping issue, when zooming out the coal "lumps" on the track disappear and are replaced with a light vanilla looking track. Since the coal lumps are only modelled on non-procedurally-generated portions of the track, it makes a really patchy look.

Would you like to add these changes into the mod? I can send you the files.

Cheers!