I'm not sure it's most of the places. Some, absolutely. But I think most of a road train's journey is along dry, open country roads.
Okay, so are you "programming a route" or are you reacting to the surroundings?
Robot trucks do both.
Note that the autonomous mining trucks used in the Christmas Creek mine (and some others) are almost entirely pre-programmed. Autonomous road vehicles have to be able to both follow a route, and react to their surroundings.
Dry country dirt roads- until its the wet season lol.....
(I know it doesn't happen a lot, but it DOES rain up here, and when it does..... well you need to be able to wield a shovel and a winch....
And like I said- programming a route can be useless, because the roads often 'shift' around, as one section get 'chewed out' drivers will drive next to it instead (because its smoother) and the road gradually moves away from its original position....
Mines maintain their roads (and many of those automated mining trucks are following 'beacons' rather than GPS or visual cues btw- lol, I have personally worked in some of those mines and even on some of the trucks fitting fuel monitoring equipment) their 'self driving' capabilities are little more than 'follow the IR 'trail' with cued stopping points...
And I both live and drive up here.... I KNOW what the roads get like in the wet season....even 4wds can get stuck, let alone cars....
That's why if you come to my place, there's the little Corolla (inherited lol- and dry weather only), two 4wds (the cruiser and the lux) and the Merc tilt-tray (its got a 18 tonne max capacity winch and a diff lock on it, not 4wd, but next best thing to it)

Seriously- most cars can't handle it- and robocars??? PMSL- yeah right.....
As for self driving road trains- we will have flying cars long before that even happens out here... the tech is decades away from being able to handle it....