The transitional property of a lemniscates curve is disrupted when its deflection angle is around  

Explanation:

Bernoulli’s Lemniscate:

• For Bernoulli’s lemniscate, the rate of change of radius is uniform up to 30° deflection angle and non-uniform beyond 30°.
• The transition behavior would be disrupted after 60° deflection angle. Therefore, it is not recommended for highways or railways.

Additional Information

Spiral Curve:

For a spiral curve, the rate of change of radius is uniform throughout the length. It is preferred for highways as it brings in faster smooth change which is most suitable for vehicular traffic movement.

LR = Constant for spiral curve

Where. L = Length of the curve and R = Radius of curve

Cubic Parabola:

For cubic parabola, the rate of change of radius is uniform up to deflection of 9°, beyond 9° the rate of change of radius is uniform but with a higher value. Since it brings in a smooth change up to 9° and railway curves do not deflect so much, it is preferred for railways.

Square Parabola:

It is recommended for vertical summit curve.