I've decided to do a long run with a truck from Serbia to Montenegro, most of the road was nice, but once I came to the mountainous regions, I couldn't drive anymore, so I had to respawn the truck after the real world tunnel finishes, since currently Outerra doesn't show tunnels as actual roads, but just forest.
The other issue, especially in Montenegro, was roads that have insane height differences, drops and climbs, so that you would need a rocket engine to climb them, I suppose that this is the same in Switzerland and other mountainous places like that.
I'm not a programmer or anything, so I have no understanding of how all that works, but still my idea is, if it is possible, for tunnels to make them (roads in tunnels) start with the height of where the tunnel begins and end with the height of the tunnel exit, the path between these two could be either direct or maybe even the same path as in real world, but the height of the medium part of the tunnel road wouldn't be important, I don't know if I explained it well, but hopefully you understand. I doubt that it is possible to get road height info inside tunnels, but it is possible to get height info on tunnel entrance and exits, so maybe they can be connected somehow.
The steep roads, crazy drops and climbs, if possible, could maybe be fixed with an algorithm that averages out the height of the road sections in case a part of the road is extremelly steep, so for example if section A is 30m above ground level, section B is 15m (a bridge,etc. that shows up like that) and section C is also 30m, then an algorithm should change section B to either 30m or something that falls into a "tolerable steepness" level. That way bridges and mountain climbs wouldn't be an obstacle anymore and perhaps people could drive in Switzerland and places like that.