This mod optimizes the game by disabling some "extra" details like the train, ai-traffic, ai people walking around randomly.
Starting with 39 to 43 fps on without the mod, I got 58 to 65 fps with the mod. I honestly didn't think that these extra things would impact fps this much.
I used this mod and it works, giving my 50-60 FPS but I tried to remove it for the new experimental ai rally cars and it added back in the random people walking around but the highway traffic is non-existent.
