A hill road may be defined as the one which passes through a terrain with a cross slope of 25% or more. There may be sections along hill roads with the cross slope less than 25%, especially when the road follows a river route.
Even then these sections are also referred to as hill roads. Hence, to establish a hill road overall terrain must be taken into account. The hilly regions generally have extremes of climatic conditions, difficult and hazardous terrains, topography and vast high altitude areas.
The region is sparsely populated and basic infrastructural facilities available in plain terrain are absent. Hence, a strong stable and feasible road must be present in hilly areas for overall development of other sectors as well.
Design and Construction Problems:
Design and Construction of roads in hills and mountain are more complex than in plain terrain. It is due to several factors associated in the region. They are:
- A hilly or mountainous area is characterized by highly broken relief with vastly differing elevations and steep slopes, deep gorges etc.
- which may unnecessarily increase road length.
- The geological condition varies from place to place.
- Hill slopes stable before construction may not be as stable due to increased human activities.
- There may be variation in hydro-geological conditions which may easily be overlooked during design and construction.
- Due to highly broken relief construction of special structures should be done at different places.
- This increases the cost of the construction.
- Variation in the climatic condition such as the change in temperature due to altitude difference, pressure variation, precipitation increases at greater height etc.
- High-speed runoff occurs due to the presence of high cross slopes.
- Filling may overload the weak soil underneath which may trigger new slides.
- The need of design of hairpin bends to attain heights.
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