Most of us know that the shortest line is the straight line connecting two points together. But in reality, roads up mountains or steep slopes are not built according to this principle. If you have the opportunity to go to the mountainous provinces, you will see and experience winding roads like this.

Some roads going up the mountain have even become famous around the world because of their winding and many turns. So why don't they build these roads in a straight line but instead make them zigzag like that?

The answer is very simple, it is to protect the lives of pedestrians, helping them easily move up slopes. In the past, in order to build a road to the top of the mountain, people often brought a donkey to let it go up the slope to explore first.

They found that this animal did not go up the shortest straight path, but instead chose a path with a moderate slope. Because this is the slope that they feel safe at (about 8 - 10 degrees). The exploration team will base on the path the animal travels, measure and sketch, and then build.

In terms of science, the reason is explained as follows. If drivers have to run uphill in a straight line for a long time, it will affect their vision. This can easily cause distraction and danger. Curvy and winding roads will stimulate drivers' concentration more.

From a geographical perspective, the terrain of mountains is often dangerous and rugged, so flattening it into an inclined line from the foot of the mountain to the top will be very difficult. It's even more costly than building a zigzag road.

From a physical perspective, based on the principle of inclined planes, a straight slope creates many dangers both up and down. If the road is curved and winding, it will reduce the speed in the downward direction and reduce the inertia in the upward direction. In case the vehicle carries many passengers and goods, it will be even more dangerous.