AC Collision rules:
Collision: Any object with a number in front of it becames physic, and the number identifies the sector number (exactly as like as in nKpro). If you call an object 01MUD then you'll have to define that name on surfaces.ini of the track. the only exception is WALL (01WALL, 02WALL ecc ecc)that is by default the mesh collider and can't be modified. There are some default definitions that could help, like ROAD, GRASS, SAND, KERB
See attached pictures from your BackwoodGarage, all "track" Objects start with number...
Take your time to see if there's something to do, no hurry, I can wait. If I can find something else I will PM to you. Thanks!