Sentence:  By encreasing the hollowness of a wide carriage road, much beyond the utility of form, the margins might no doubt be brought into a travellable state; whereas, of a flat road, in a wet season, every part, from side to side becomes equally <WSD>untravellable</WSD>. 
Meaning of the word marked with <WSD> tags:  Unsuitable for or hostile to travel; incapable of being journeyed over or upon.