This reads like an LOD (Level Of Detail) issue in the track itself. Since it is a track issue, then changing the Trainz settings will not solve the problem.
In case you are not aware of LOD, it is how content creators can alter the visual appearance of an object (e.g. a house) so that it shows less detail and uses fewer GPU resources the further away it is from the camera. LOD is now a strongly recommended requirement (i.e. it will eventually become compulsory) of all scenery objects including track. Unfortunately, some track assets use LOD very poorly so the transitions between the different detail levels are very obvious. Track has the disadvantage that it exists from the camera position right out to infinity so that there is no really easy way to hide the places at which the transitions occur, but some track creators are better at this than others.
If it is an LOD issue, then the best solution may be to try different track assets (from different creators) to see which ones handle this issue better.
