that would be 100 physic-objects, from my testings that wont work good (if its not a very fast pc)
i once tried to built a house out of physic-objects (single stones), but specially at startup it was slower then a slideshow. so i think you should test it and see what happens.

you could try to let the ai-cars only have physics enabled when near to the camera, wouldnt that work?

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