The main factors to be considered while deciding the alignment of hill roads, are given below.
The cost of construction of a hill road per kilometer length is comparatively very high. It should therefore be ensured that length of the road connecting two stations should be minimum possible, adopting ruling gradient along its most of the length.
2.Altitude of the Road
At lower altitudes, large numbers of cross drainage works are required to be constructed. Whereas at higher altitudes, the road pavement may witness snowfall during winter. This is why the alignment of hill roads should preferably be provided at an altitude between 900 m slopes exposed to sun. The hill slopes which are subjected to high winds should never be selected unless and until there is no other alternative. In northern hemisphere, southern slopes of the hills are more suitable than northern slopes which remain tin shades and are usually subjected to high winds.
3.Saddles or Passes
While locating contour gradient of the proposed alignment of a hill road on a contour map, it should cross the ranges through saddles. Though length of the road is increased, the heavy cost of cutting through rocks is avoided. Due to increased length, ruling gradients can be suitably adjusted.
4.Stability of Hill Slope
While deciding the alignment of hill roads, it should be ensured that the slopes are stable and not very steep. The area is not prone to landslides and settlements. This factor is of special importance in hills having sedimentary rocks.
Cutting through solid hard rocks is very expensive. The alignment of roads may be suitably deviated to avoid such areas.
Drilling of tunnels is very expensive. The long tunnels needed ventilation as well as lighting arrangement. As far as possible, tunnels should be avoided and resorted to only if other suitable alternative is not feasible.
While deciding the alignment for crossing a river valley, due consideration should be given to avoid construction of a number of bridges on its attributes.
The alignment of the hill roads should be selected on the hill slope which easily provides recommended geometric standards i.e. gradients, curves, sight distance etc. Hairpin bends on roads should be avoided and if found necessary, these should be on gentle and stable slopes. To have proper geometric standards, it might be necessary to change the alignment at number of places.
At intermittent distance, the alignment of the hill road should pass through gentle slopes where suitable camping sites could be developed for military personnel in case of necessity.