I found this video today, It's Remote Control cars that real very realistic. The guy filmed himself driving both of them. How did he edit them so it looked like they were both there at the same time? I've heard of Garbage Matts but when I use matts I can't get something to be in front or behind an object without part of the video cutting off. https://www.youtube.com/watch?v=60KvhR8fZHw
Hilarious video (that guy needs a horn in the truck for Oranges the Cat (bridge scene))
It looks like most of those shots are completed using simple garbage masks (or mattes) to reveal one take over the other.
The detail on those RC trucks (including the arm out the window) is excellent.
Setting up the shoot is important. He probably has both trucks ready (notice that they start off camera).
Locked off camera / lights
Drive one of the trucks through the scene.
pick up the other remote and drive the other through the scene.
In After Effects or PremierePro, edit/time-remap the trucks so they don't drive in the same location at the same time. You can do this with transparency turned down on one of the layers.
Then, it's just a matter of rotoscoping one of the trucks.
This works relatively well as long as the background doesn't change notably.