As per IRC, the minimum length of transition curve for a mountainous terrain road with radius of curvature 100 m and design speed of vehicle 100 kmph is

Concept: 

Length of transition curve 

Based on IRC Formula

 for Hilly terrain and  for Plain and Rolling terrain.

Where

Ls = length of the transition curve (m),  V = speed of the vehicle (km/hour),

 R = radius of the transition (m),

Calculation:

Given,

Design Speed = 100 kmph, Radius (R) = 100 m

iii) By empirical formula

For Mountainous or Hilly Terrain 

∴ The length of the transition curve-based IRC empirical formula is 100 m

Additional InformationLength of transition curve (Maximum value is to be considered among the below options)

a) Based on the rate of change of centrifugal acceleration (c)

where  ……….. c value should be between 0.5 to 0.8

b) Based on the rate of change of superelevation (e)

1. Superelevation attained by rotation about the inner edge or outer edge

2. Superelevation attained by rotation about the center

c) Based on IRC Formula

 for Hilly terrain and  for Plain and Rolling terrain.

Where

Ls = length of the transition curve (m), v = speed of the vehicle (m/s), V = speed of the vehicle (km/hour),

e = required superelevation, N = rate of change of superelevation to be attained, R = radius of the transition (m), and

w = width of road/pavement