Right, I'm suggesting that there is a bit of artistic license taken here in the art by having perfectly smooth tops to these red cabs, with nothing in the narrow space visible above them.
These could very well just be rolling along a track on the floor, and I could be totally wrong. I just am thinking of other load areas on other rides, and normally when it rolls on the floor, there is a big open space above the track. (I'm thinking Snow White, Pinocchio, Mr. Toad, Haunted Mansion, Buzz, Ariel, etc.) But this art is giving me a Peter Pan vibe: The space directly above the vehicles is walled up, and "out of frame" so to speak.