If you are "hiding" collision meshes, collisions can't happen on those parts. I "UNhide" collision meshes when a vehicle gets near it and "hide" it again when the vehicle leaves it. You have to ensure your logic doesn't eat up the advantages of this though.
if your collision mesh is of low enough poly you won't need to worry about it though!
if your collision mesh is of low enough poly you won't need to worry about it though!