Length of Transition Curves
Transition curves are provided in between a straight road and the Curve of a design radius.
The radius of a transition curve varies from infinity to the design radius or vice verse. The length of the transition curve must fulfil some requirements. It is designed to fulfil the following three conditions.
The radius of a transition curve varies from infinity to the design radius or vice verse. The length of the transition curve must fulfil some requirements. It is designed to fulfil the following three conditions.
(a) Rate of Change of Centrifugal Acceleration(C)
C = (v^2/R)/t = (v^2/R)/ (Ls/v) = v^3/( LsR) m/sec^3
As per IRC recommendations, C= 80/(75+v) m/sec^3
Here, C= allowable rate of change of centrifugal acceleration ( m/sec^3)
Ls= Length of the transition curve.
Read: Length of the Summit Curves(Vertical Curves)
(b) Rate of the introduction of Designed super-elevation
If the pavement is rotated about the centre line, then
1/N = (E/2)/Ls
=> Ls= EN/2 = e.B.N/2 = e.(W+We).N/2
If the pavement is rotated about the inner edge, then
1/N = E/Ls
=> Ls= EN = e.B.N= e.(W+We).N
where, Ls= Length of transition curve
B= width of the pavement
(c) By Empirical Formula given by IRC(Indian Roads Congress)
It should not be less than
(i) For plain and ruling terrain: Ls = 2.7 V^2/R
(i) For plain and ruling terrain: Ls = 2.7 V^2/R
(ii) For mountainous and steep terrain: Ls = V^2/R
Find out the greatest length of the transition curve by the above three criteria and use to construct the transition curve.
Read: Length of the Summit Curves(Vertical Curves)
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