You actually don't see the car. You see the dust the car raises. It is when Sam is standing in front of the scarecrow telling Frodo that one more step will lead him further than he has ever gone.
I have looked and looked at that "dust" and am convinced it's smoke from a hobbit hole fireplace. I believe I saw Gollum yesterday at the Argonath. He is lying in the lower lid of the the king's eye, you only get a tiny glimpse of him right before the birds fly out.
Yes, I'm a big fan of these books and never found a single thing, no miniature, illustration or anything that compared to my imagination until this movie came out. The first time I saw it, I was completely speechless and couldn't even form the words for days afterward to describe the feeling. It was like the workings of my mind were being projected up onto the screen. Quite an event for me. I've been reading these books for 30 years and when I was in high school, I figured out the elvish language. I've since forgotten it.
I didn't see any 'dust', but i did see the sun 'glint' off the side of the car as it was passing by....