Correct Answer : clothoid spiral
Explanation : IRC recommends Spiral or clothoid as the ideal transition curve due to following reasons:
1. It satisfies that rate of change of centrifugal acceleration is constant i.e., Ls.R = constant. Where Ls = length of transition curve R = radius of curve.
2. The calculation and field implementation of spiral curve is simple and easy.
3. It enhances aesthetics also.
