Sorry, no update yet. But I will try to give a few answers and comments.
I used LDraw Tools to create two files. One is the 'mesh' of the track, the other one is the colliding map.
I wrote a little bit of source code, that creates the GDB and BDB files out of the 'mesh' file and the BVB file out of the colliding map. But currently you have to respect a lot of rules to create a working result. The process is absolutely not user friendly and I did not wrote down any rules or tutorials by now. Today, I do not know a simple way to create tracks. A lot of work was done manually!
Here are two images of the LDraw files:
This is the 'mesh' file. You have to respect the back face curling. The different colors are for different textures (black -> 0 -> first texture; blue -> 1 -> second texture, aso...). There is no chance to create vertex colors!
This is the colliding map. Here you also have to respect the back face curling (here green is the front side, red is the back side). I removed the bottom plane so that you can see something. This is the base for the tree in the BDB file. The game will not let you drive through a triangle from the front to the back; but the other way around.