Geo metrics of hill Roads
the roads in hills need special attention in fixing up geometric standard for gradient, super elevation, radius of curvature etc. which are different from those in plains.
The main reasons for the difference are the topography and other problems in alignment of hill road.
The following modifications are necessary from hill roads point of view.
Width of carriage way
a minimum width of 3.75 m may be adopted for the pavement road or Carriageway is unmetalled but carries motor traffic. A width of 3 m will suit the jeep able roads.
Formation Width
the formation width in hill roads depends more upon the type of vehicles plying on it.
a) The formation Width for motor able road carrying a total load less than 100 tonnes per day is 7.5 meter on straight and 11 metre on curve.
b) The formation Width for motor able road carrying a total load between 100 tonnes to 400 tonnes and above per day is 4.5 to 5 meter on straight and 7.25 meter on curves.
Camber or Cross Slope
The hill roads are provided steeper camber or cross slope. When the road has longitudinal gradients greater than 1 in 20, flatter camber may be provided.
Sight Distance
The minimum sight distance required will be stopping sight conforming to the design speed of the road.
Curve Radius
in initial stages of construction, no curve shall have a radius less than 30 m. each curve must have transitions on the two sides, as far as possible.
Super elevation
the minimum super elevation the minimum super elevation on hill roads should not exceed 10 percent (1 in 10) and 7 percent (1 in 15 ) in snow bound sections.
Gradients
at horizontal curves, the percentage compensation in gradient may be provided using the formula (30+R/R) with a maximum of 75/R. The compensated gradient may not be flatter than 4 percent.
