Thanks for your reply, I had actually previously tried the usual Xform modifier (got inspiration for that from other forums), but didn't obviously work. Now after some tinkering the settings of the UVW Xform modifier I got it working in game finally. Thanks a lot for the advice![..]
Glad you've worked it out

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[..]Now about the track side texturing, I do am familiar with it in the texture creation level (diffuse, normal, specular, detail and alpha/RGB blendings etc.), and could easily map it to straight geometry section, but how to map such transfer areas on curvy road section sides? Is it with Spline Mapping again, or Z-axis Unwrap UVW (manually creating curved texture in PS) or am I missing something here?[..]
I am using Blender myself, I'm not perfectly aware of the function you need to use in max. However, I can share the concept, definitely it's possible to do the same in max.
In Blender there is an unwrapping function called Follow active quads, ehich will follow the ngons of your mesh, instead of the absolute geometry. This way the mapping will actually go with the flow of the road, no matter how twisty it is. This is especially true for an existing geometry.
A second method is to first create a basic road section, and texture it before you apply any array modifiers to it. Later when you actually apply your modifiers, the mapping should be automatically generated and it will follow the road.
Hope this can help you in some sort.
[..]Also, what is the benefit of dividing track geometry into separate pieces, as done in Newbury sample track?
It is required in order to allow the AC engine to optimize the performance. This way only the parts of the track which are visible/need to be drawn at one point in time are loaded into memory, thus allowing for better use of resources. This is a process which is done dynamically and automatically, only thing you need to worry is to split your mesh

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It might not matter much in a simple/small track; but think about a huge one, like Nordschleife
There are actually a few other tricks you can do in order to help having better frame rates:
- use only dds textures
- use the
naming convention for the trees, so they can be automatically grouped (and lit sparing you the trouble of setting up normals manually)
- put objects like 3d grass on different layers so they can be showed or not, according to world detail settings
..and one which is a bit more difficult but necessary in case you are talking about a couple of millions tris track, is the use of LODs.