Looking at some installed examples, I agree, there's no LOD even in the latest (trainz-build 3.5) "YARNish" roads, let alone in the original YARN roads by Maddy25.
However, this does not explain why they "drop out" at a distance of just 50-100 feet in TRS19. Have N3V suddenly implemented some really harsh spline-culling rules? If so it would really make a lot of legacy assets essentially useless in TRS19.
.
Currently I use the JR Road pack which also have no LOD done and don't suffer any drop-out from any distance. I don't think that there has been any changes to the spline culling code.
Example config from one of my old roads on the DLS which are build 2.9 and need updating for TRS2019:
mesh-table
{
lod0
{
mesh "double-line-y-lod0.im"
}
lod1
{
mesh "double-line-y-lod1.im"
}
lod2
{
mesh "double-line-y-lod2.im"
}
lod3
{
mesh "double-line-y-lod3.im"
}
}
track
{
mesh-length 40
adjust-cross-section-to-ground 1
track-lod-tree
{
lod-distance 400
high-detail
{
lod-tessellation-length 10
lod-length 10
high-detail
{
lod-tessellation-length 5
lod-length 5
high-detail
{
subdivisions 8
mesh "lod0"
}
low-detail
{
subdivisions 4
mesh "lod1"
}
}
low-detail
{
lod-tessellation-length 20
lod-length 20
high-detail
{
subdivisions 2
mesh "lod2"
}
low-detail
{
mesh "lod3"
}
}
}
low-detail
{
lod-distance 400
high-detail
{
lod-tessellation-length 10
lod-length 10
high-detail
{
subdivisions 4
mesh "lod1"
}
low-detail
{
lod-tessellation-length 20
lod-length 20
high-detail
{
subdivisions 2
mesh "lod2"
}
low-detail
{
mesh "lod3"
}
}
}
low-detail
{
lod-distance 800
high-detail
{
lod-tessellation-length 20
lod-length 20
high-detail
{
subdivisions 2
mesh "lod2"
}
low-detail
{
mesh "lod3"
}
}
low-detail
{
mesh "lod3"
}
}
}
}
}
With that setup, I get nice smooth curves and even used on PBR Ground textures it hugs the ground in most cases.