TRANSITION CURVE IN HIGHWAY | OBJECTIVE | TYPE| CALCULATION

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TRANSITION CURVE IN HIGHWAY | OBJECTIVE | TYPE| CALCULATION

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TRANSITION CURVE
It is provide in between straight and circular so that radius is gradually from infinite to R. 

Objective of transition curve 

1> To gradually introduce the centrifugal force in between straight and circular .

2> To gradually introduce super elevation and extra widening .

3> To avoid sudden jerk .

4> To enable the driven to turn the steering  of vehicle gradually for comfort and security .

5> Aesthetic purpose 

   Types of transition curve

credit : Civil Ganeshwar
1> Spiral or clothoid (highway)
2> Bernoulis lemniscate 
3> Cubic parabola ( railway )
Ideal shape of for transition  spiral clothiod because rate of change of centrifugal acceleration is constant throughout.

note : For small deviation  angle behaviour of all the three types of transition curve are same .

LENGTH OF TRANSITION CURVE 

1> Based on rate of change of centrifugal acceleration  
                LS =( V^3)/CR                   where V is in Kmph
where c = 80/(75+ V )         .5⥶ c ⥶ .8  where c is in m/s^3
2> Based on  rate introduction of super elevation  and extra widening 
      case A> Pavement is rotate about centre 
1/N =Rate of change of superelevation
    case B> when pavement is rotate about inner edge 
Ls = eN(w+we)

3> Empirical formula 
  Ls = 2.7V^2/R ( plain and rolling area )
       = V^2/R  (hilly area )
As per IRC :
1> N= 150 for plain and rolling terrain
2> N= 100 for built up  area 
3> N = 60 for hilly area 
 Length of transition curve taken minimum value from case 1,case 2 and  case 3 .

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