Civil Engineering - GATE Exam Questions - Discussion

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.

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.

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.

The circular curve is the ideal form of summit curve because of in circular summit curve sight distance available throughout the length of the circular curve is constant.

But in practice, generally, use square parabolic curve because it is easy to compute and also give riding comfort.

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.

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.

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.

Here according to me spiral curve because rate of according of centrifugal force is constant. This case not satisfied in parabola, lemniscate.

The circular curve is correct. Because ideal shape is circle, provided shape-parabola. It is the correct one.