The length of the transition curve should be determined as the maximum of the following three criteria: rate of change of centrifugal acceleration, rate of change of superelevation, and an empirical formula given by IRC.

**Length of
transition curve**

The length of the transition curve should be
determined as the maximum of the following three criteria: rate of change of
centrifugal acceleration, rate of change of superelevation, and an empirical
formula given by IRC.

Rate of
change of centrifugal acceleration

At the tangent point, radius is infinity and hence
centrifugal acceleration is zero. At the end of the transition, the radius R
has minimum value R. The rate of change of centrifugal acceleration should be
adopted such that the design should not cause discomfort to the drivers. If c
is the rate of change of centrifugal acceleration, it is given by an empirical
formula suggested by by IRC

**Vertical
alignment**

The
vertical alignment of a road consists of gradients(straight lines in a vertical
plane) and vertical curves. The vertical alignment is usually drawn as a pro
le, which is a graph with elevation as vertical axis and the horizontal
distance along the centre line of the road as the the horizontal axis. Just as
a circular curve is used to connect horizontal straight stretches of road,
vertical curves connect two gradients. When these two curves meet, they form
either convex or concave. The former is called a summit curve, while the latter
is called a valley curve.

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