Civil Engineering - GATE Exam Questions - Discussion

Ideal shape of summit curve is circular.

But Square parabola is the best shape of the summit curve due to good riding qualities, simplicity of calculation, and uniform rate of change of grade.

Ideal shape: Circular.

Preferable shape: Parabolic.

Many curve forms can be used with satisfactory results, the common practice has been to use parabolic curves in summit curves. This is primarily because of the ease with it can be laid out as well as allowing a comfortable transition from one gradient to another. Although a circular curve offers equal sight distance at every point on the curve, for very small deviation angles a circular curve and parabolic curves are almost congruent. Furthermore, the use of parabolic curves were found to give excellent riding comfort.

For horizontal alignment, ideal curve is a spiral.
And for vertical alignment ideal curve is a cubic parabola.
Here, the summit curve is vertical alignment so the parabola is the right one.

Circular curve is the right answer because of uniform sight distance.

Circle is the right answer.

The Answer is C.

Because the question is about ideal shape not about good comfort or what is the shape of summit curve in actual practice.

In actual practice, the shape is preferred as simple parabolic (real life) instead of circular so as to provide good riding comfort.

Ideal shape is circular because it gives sight distance constant throughout tge length of the circular curve. But considering the good riding comfort, in practice simple parabolic curve is used as summit curve.

An Ideal shape is circular.

Ideal shape for Summit curve is Circular because side distance is constant.