Although you're driving along narrow mountain roads, you'll feel much safer than in the plains, because everyone takes infinitely more care; lorry and bus drivers are clearly subdued by the deep ravines.
The people in the plains are careless drivers.  
mnli hypothesis: The people in the plains are careless drivers.   premise: Although you're driving along narrow mountain roads, you'll feel much safer than in the plains, because everyone takes infinitely more care; lorry and bus drivers are clearly subdued by the deep ravines.