Why are mountain roads generally made winding upwards rather than going straight up ?

Explanation

While going up a mountain the opposing force of friction ` F = mu R = mu mg cos 0 ` where `0` is angle of slope with horizontal To avoid skidding , `F` should be large
`:. cos theta` should be large and hence `theta` must be small That is why mountain roads are generally made winding upwards. The road straight up would have larger slope .