Cars want to run up from the mountain’s foot, cannot run vertically, always follow the winding road to run up the mountain. In doing so, not only does the vehicle run relatively safely, but it also saves effort.
We almost all realize: walking or riding a bicycle from a low place to a higher place is harder than walking on flat land; climbing a steep slope will take more energy than a gentle slope. Therefore, when going up the slope, people always find a way to reduce the ridge’s slope a little. For a ridge with a certain height, the longer the ridge’s slope is, the smaller the slope. Therefore, people often use the way of extending the slope to reduce the slope, achieving less effort.
For example, when pushing a heavy cargo cart up the slope, you will feel very tired if you straighten it up. Experienced people often push up in the S shape. Thus, although there is a little extra road length, it can take a lot of energy. Going up the slope in an S-shaped shape means making the slope longer, reducing the slope.
There is another example, at both ends of a large and high bridge has a long path to the bridge, sometimes built a spiral path. It is all to reduce the slope of the bridge but to extend the bridge surface.