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

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

**For Equilibrium**

R= Radius in m

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.**

### A. Rotation about Centre line:

**B. Rotation of pavement about the inner edge**: Outer edge of the pavement is raised by e

Ruling minimum radius of horizontal curve :

, where V= ruling design speed (kmph)

**Ruling minimum radius**

For N.H. & S.H. | 360 m |

For M.D.R | 230 m |

For O.D.R | 155 m |

For V.R | 90 m |

Superelevation

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