If these are all tagged as Collision they may kill frame rates on impact for everyone nearby regardless of what car hits them. While 'walking' around your track I noticed bunches of tires. It looks like there is a problem with sobj_14.gmt. So the good news is I can open you scn in 3dsimed 1.18a. I wish BTB would accept gmt objects, because some of what you have is fine, and would make rebuilding the project back to where it should be that much quicker. Worst case scenario is you have to do this one by one with a load of 3dsimed or rf in between. You may have to copy good scn entries out of the archived version into a newly extracted. Like I said the cones, walls, and track surface are good. I would set aside the Schenley folder and contents you currently have for safe keeping. It is the only method I've seen here for recovery of a project that won't open. Moving forward in this case involves stepping back to an earlier backup where you had not so many objects. All I know is there were a lot of things to import. I have no clue if there is a limit on the number of materials in a track. While importing it almost looked like 1 object=1 material. It very well could be that the import script is duplicating materials. Once you get back to editing double check your xsectors, one of them doesn't intersect the ground plane and could be missed, I didn't check the other 2. At 397 material names, and thousands of objects and millions of polygons the entire track is taking huge amounts of memory to open, so much so that it is crashing max. Since I am falling asleep I'll see if I can get you a list of textureless objects later this week. Hopefully you have an earlier version that opens in BTB. I would use tga if you can't be bothered to convert to dds. If I had to guess I'd say the png textures are doing it. There is a car mesh (obj_49) with no texture.
![3dsimed export obj 3dsimed export obj](https://pbs.twimg.com/media/EdAi-_XU0AAQLJh.png)
A lot of the other "tree-looking polygons" are not showing any textures. obj_429.gmt has material roada1508 assigned to it although there are no textures assigned to any of the shader levels.
![3dsimed export obj 3dsimed export obj](http://sim-garage.co.uk/wp-content/uploads/11-09-2017-20-49-35.jpg)
It looks like something went fubar with materials. It is really hard to say what went wrong. I got everything, Cones, Nightglow, Walls, obj, objc, (and the rest) to import. I separated meshes into groups by name to see if I could break down what objects are causing the problem.