> Not sure this is a good example : elevation data should be good enough to avoid this kind of roads.
I'm not sure elevation data is enough, nor is speed limit. In many places, like the Cotswolds, the main route includes a 20% gradient. The difference is the road will be wide with overtaking lanes etc. and often a reduced speed limit. Then you have places like Devon where there are national speed limit (the highest) roads with such poor visibility they are best avoided unless you have no other choice. I find it's hard to know what the quality or "character" of a road will be until you actually get there, but Google seems to treat them all equally.
I'm not sure elevation data is enough, nor is speed limit. In many places, like the Cotswolds, the main route includes a 20% gradient. The difference is the road will be wide with overtaking lanes etc. and often a reduced speed limit. Then you have places like Devon where there are national speed limit (the highest) roads with such poor visibility they are best avoided unless you have no other choice. I find it's hard to know what the quality or "character" of a road will be until you actually get there, but Google seems to treat them all equally.