The main factors to be considered while deciding the alignment of hill roads are given below.
The cost of construction of hill road per kilometer long is comparatively very high. Therefore it should be ensured that the length of the road connecting the two stations is as short as possible, adopting the ruling gradient along its maximum length.
At low altitudes, a large number of cross drainage works need to be constructed. Whereas at higher altitudes, road sidewalks may receive snowfall during winter. This is why the alignment of hill roads should preferably be provided at a height between 900 m of slopes exposed to the sun. Hill slopes subject to high winds should not be chosen unless there is no other option. In the Northern Hemisphere, the southern slopes of hills are more suitable than the northern slopes which remain tin colored and are generally subject to strong winds.
3.saddle or pass
When tracing the contour gradient of a proposed alignment of a mountain road on a contour map, it must cross the ranges by means of saddles. Although the length of the road has been increased, the huge cost of cutting rocks is being avoided. Due to the increased length, the ruling gradients can be adjusted as appropriate.
4.hill slope stability
While deciding the alignment of hill roads, it should be ensured that the slopes are stable and not too steep. The area is not prone to landslides and settlements. This factor is of particular importance in hills with sedimentary rocks.
Cutting solid hard rocks is very expensive. The alignment of roads may be suitably deviated to avoid such areas.
Drilling of tunnels is very expensive. Long tunnels require ventilation as well as lighting. Tunnels should be avoided as far as possible and resorted to only when other suitable alternatives are not possible.
While deciding the alignment to cross the river valley, its features should be given due consideration to avoid the construction of multiple bridges.
The alignment of hill roads should be chosen on a hill slope that easily provides recommended geometric parameters such as gradients, curves, sight distance, etc. Hairpin bends should be avoided on roads and, if necessary, on gentle and steep slopes. For proper geometric parameters, it may be necessary to change the alignment in several places.
At intermittent distances, the alignment of the mountain road should pass through gentle slopes where suitable camp sites for military personnel can be developed if required.