3.3.1 CAMBER


Camber is the transverse slope of carriageway provided to the road surface for the drainage of the rainwater for the better performance of road. Camber can be written as (1 in n or x %). According to NRS 2070, camber shall be of following characteristics:

  • All straight section of roads shall have a camber or cross fall.
  • To remove water from road surface as quickly as possible.
  • To protect the road by preventing the entry of surface water to the subgrade soil through the pavement.
Pavement typeEarthenGravelBituminousConcrete
Camber5%4%2.5%1.5% to 2%

3.3.2 SUPER ELEVATION



Super elevation or banking is the transverse slope provided at the horizontal curves to counter act the centrifugal force by raising the outer edge of pavement with respect to inner edge throughout the length of horizontal curve. Superelevation helps to resist the skidding of vehicle during turning through the curve. Superelevation depends on the design speed, radius of curve, coefficient of friction between vehicle type and road, etc. Superelevation is provided to reduce the tendency of vehicle to overturn and to skid laterally outwards by raising the pavement outer edge with respect to inner edge.



Value of superelevation is calculated using following formula

e+f = V2/gR

where,

e = superelevation of curve ( % )

f= coefficient of lateral friction

V= Design speed (m/sec)

g=acceleration due to gravity (9.8 m/s2)

R=radius of curve (m)

When, speed of vehicle is in KMPH.

e+f = V2/127R

According to NRS 2070 maximum superelevation is to be provided is limited to

  • In plain and rolling terrain = 7%
  • In snow bound areas = 7%
  • in hilly areas not bound by snow = 10%

3.3.3 EXTRA WIDENING

Extra widening can be defined as the additional width of carriageway, which is required on curve section of road that on straight alignment. It is required because.

  • There is tendency of driver to take the outer path at the curves to have more sight distance visible ahead.
  • While overtaking operations on horizontal curve driver will need more spacing from the other vehicles to feel safer.


Extra widening depend on

  • Length of wheel base
  • Radius of the horizontal curve
  • Psychological factor which depends upon the velocity of the vehicle and the radius of the curve.

Extra widening = Mechanical widening + Psychological widening

We = Wm + Wpsy  = nl2/2R + V/2.64√R where V is in m/s

We = Wm + Wpsy  = nl2/2R + V/9.5√R where V is in km/hr

Where,

n= number of traffic lanes

l= length of wheel base

R= radius of curve in m

V= speed of the vehicle