How do they decide the way mountain roads twist and turn?
In: 200
The short answer is that they follow the landscape. In flat areas you can simply build a road relatively straight from your origin to destination, with a few gentle curves going around obstacles. In steep mountains, going in a straight line would mean going straight up and down cliffs and steep slopes. However heavy trucks can only go up a relatively gentle slope of 10% or 1 in 10. If you have lots of resources, you can build bridges over the canyons, and tunnels through the mountains so that the road is nice and straight. However the cheapest place to build a road is on the existing ground surface, following all the little ridges and gullies. A road going through a gorge will have to follow the twists and turns lf the gorge.
[This map](https://www.topomap.co.nz/NZTopoMap?v=2&ll=-41.029361,172.930947&z=14) shows a twisting mountain road. It also shows the contour lines of the landscape and you can see that they are very similar. This road is following all the little ridges and valleys. [This road](https://www.topomap.co.nz/NZTopoMap?v=2&ll=-44.818691,168.108161&z=14) is also following the contour lines, but since there are less ridges and gullies, it has less curves.
Here is an example of where bridges, tunnels, and cuts into the hillside have been used to make the road straighter. [SH1](https://www.topomap.co.nz/NZTopoMap?v=2&ll=-36.555132,174.678681&z=14)
In the far eastern parts of India, there are areas where you can barely see the terrain.
There’s an old story about a young land assessor was sent out to plan the route to the next village, for the road to be built. Old hands told him to just follow the elephants. He struggled for a month before breaking down and following the elephants. Yup, they know the best routes.
In Corsica to build a road you bring a donkey to destination, then you let the donkey get back home, following it tracing the future road. If you do not have a donkey, get an engineer
For starters it matters what you begin with. A lot of those roads are made on top of existing paths or trails but even if there’s nothing the morphology of the mountainside dictates the general shape of the road. Also depending on how easy or hard it is to actually make the road dictates whether it might be rerouted from somewhere else. The ground, the slope, rocks, boulders and so on all play a role in how easy or hard it is to make the road. Lastly the gradient of the road is a very important factor which leads to engineers often adding many turns to make the slope more shallow. That’s when you see all those successive switchback hairpins for example.
To add to that: how do they decide which roads will just be steep hills and others, they’ll cut into the mountain?
Latest Answers