Superelevation

Superelevation is the transverse slope to counteract the centrifugal force and reduce the tendency of the vehicle to overturn or Skid.

where,
B= Pavement width
E= Relative elevation of the outer edge.

Calculation of superelevation :

Force acting on a vehicle moving on circular curve radius R .with speed V m/sec

1. Centrifugal force P acts horizontally outward through C.G
2. The weight of the vehicle acts vertically through C.G
3. The frictional force acts inward to the center of the curve

For Equilibrium

e= Rate of superelevation= tan$\theta$
f= Design value of lateral friction=0.15

Super elevation design:

Step-1: The super elevation for 75% of design speed (Vkmph) is calculated ignoring the friction.

Step-2: If the calculated value of “e” is less than 7% (0.07), the value so obtained is provided and if the value exceeds the 0.07 then provide the maximum super elevation i.e. 0.07 and proceed with steps iii & iv.

Step-3 : Then check the coefficient of friction f for maximum value of e=0.07 at the full value of design speed.

If f<0.15 the value of e=0.07 is safe else restrict the speed as given in next step.

Step-4 : Find the allowable speed V (kmph) at the Curve by

• If the allowable speed Va is higher than the design speed V then the design is adequate and provide =0.07 & f = 0.15.
• If the Va<V, then the sped is limited to Va kmph and appropriate warning sign & speed limits signs are installed.
• Maximum super elevation IRC recommends emax=0.07(7%) for plain and rolling terrain Minimum super elevation IRC recommends emin=Camber from drainage considerations
• Attainment of superelevation: The full S.E is attained by the end of the transition curve or at the beginning of the circular curve.

There are two methods of rotating after eliminating camber.