I used sidewalk chalk on the driveway to make some categories of where vehicles travel. I chose tracks, air (which I later changed to sky because that made more sense to Trip), road, water, and dirt. I also made a category called Cars Movie since Trip has several Cars characters, but he didn't like having those cars separate from the other vehicles that travel on roads, so we didn't really use it.
I showed Trip the different categories, then we started sorting his vehicles.
Once we were done sorting, Trip carefully lined up all of the cars on the road.