This question was previously asked in

MPSC AE CE Mains 2017 Official (Paper 2)

Option 2 : Cubic parabola

**Explanation****:**

**Transition curve:**

The curve provided on the road or on the rails at the junction of a straight line and a circular curve, whose radius of curvature changes from infinite at the straight line to a fixed value at the circular portion is known as the transition curve.

- It is provided to change the radius gradually so that the effect of curvature can be reduced on the passengers as well as on the vehicle.
- It is also used to introduce the super-elevation gradually.

Different type of transition curves are adopted by different organisations according to their specific needs and arrangement, such as;

- Euler's spiral
- Cubical spiral
- Cubic parabola
- Lemniscate curve

__Important Points__

**Cubic parabola: **The equation for this curve is L = \(\frac{x^3}{6\times R\times y}\) [y = ordinate; x = abscissa; R = Radius of curvature, L = Length of transition curve]