I prefer to map cap parks as areas, and then I add one-way service roads for the entrance and exit, that link the road and the perimeter of the car park, thus leaving no through route.
I do sometimes mark out the main “roads” in big ground-level car parks, but if the entrance and exit are on different roads and you’re concerned about routing programs sending people through them, don’t add these, or add access = permissive/private or something.