OK thanks, as I said this was weird, appreciate your time and comments. Maybe because I am adding more objects like airport clutter, people and grass to the airport it somehow impacted the ability (slowed down) the loading of the cars. I'll just keep an eye on that.
Just thinking though it would be useful to have the shadow effect actually attached to the car object so that the parking lot doesn't get the black square effect when the cars don't show, or have the shadow also come into effect at the same time as the cars.
cheers
Bryan