It is perl. But the idea is the same for most languages. Most of them have if/else/elseif statements.
So, in a nutshell, 2-4 computers on each vehicle telling it what to do and reporting back to the main computer what it is doing and where it is. Main also send messages back to each vehicle that it either likes or dislikes what it is doing. So, in code talk: if (everything is fine with your vehicle and it is reporting well) keep going. if (something sucks with one vehicle and it has stopped even though all the others are still moving, please kill all vehicles)
Sorry if some of you thought that was a waste of space. But I was trying to impress upon you how very very complicated this is. Every scene has multiple computers, each vehicle has multiple computers and they all have to report back to one computer that calls the ultimate shots. I was just trying to tell you that this is not child's play at all. There are programmers going over code like crazy asking, "Do we need this/that?" They are parsing the code bigtime.