bumpiness

Given the bumpiness of the road ahead, you might be better off with a crash helmet.

到你面前这条颠簸的路，你最好还是配个头。

So the bumpiness, the rising high altitude, and the long duration of these two things made this short distance of the road the toughest.

岖不平的路，逐步升高的海拔，和很长的持续时间使这段路程成为了最艰难的一段。