Length of a Transition Curve (With Example) | Curves|Surveying

The length of a transition curve may be determined in the following ways:

1. The length may be arbitrarily assumed on the basis of experience and judgement as say, 100 m.

2. The length may be such that the super-elevation is applied at a uniform rate of 1 in 300 to 1 in 1200. If h is the amount of super ­elevation, then the length of the transition curve may be from 300ft to 1200ft.

3. The length of the transition curve may be such that the super elevation is applied at an arbitrary time rate of ‘a’ cm/sec. The value of ‘a’ usually varies from 2.5 cm to 5 cm.

Let:

L = the length of the transition curve in metres,

v = the speed in metres/sec.

h= the amount of super-elevation in centimetres.

a = the time rate.

Then the time taken by a vehicle in passing over the length of the transition curve 

4. The length of the transition curve may be such that rate of change of radial acceleration does not exceed a certain value, which is generally 30 cm/sec². This helps in smooth moving of the vehicles when passing over the curve, and the passengers will not feel any sensation of discomfort.

Let: 

L= the length of the transition curve

v= the spend in meters

R= the radius of the curve in meter

C=the rate of change of radial acceleration in meters/sec²

Then the radial acceleration on the circular curve=

Time taken by a vehicle to pass over the transition curve =