Horizontal Alignment and Superelevation Questions and Answers

Q: The shift of the curve(all in meter units if 'L' is length of the long chord and 'R' is the radius of curve) is:-

The shift is \(L^2/24R\).When a transition curve is inserted, the circular curve has to be moved inward by the shift\[ S = \frac{L^2}{24R} \]where L is the length of the transition curve and R the radius of the circular curve. (The stem calls L the long chord.) \(L^2/6R\) is the offset at the end of the transition curve, four times the shift, and \(L^2/2R\) is the offset of a simple curve, so they are the usual traps.

Q: Psychological Widening in the extra width provided in the pavement on the curves is:(symbols have their usual meaning)

Psychological widening is \(V/9.5\sqrt{R}\).On curves, drivers tend to keep a greater clearance from the vehicle alongside, so IRC adds a psychological widening in metres:\[ W_{ps} = \frac{V}{9.5\sqrt{R}} \]with V in km/h and R in metres. The total extra width is this plus the mechanical widening \(nl^{2}/2R\), which allows for the rear wheels tracking inside the front wheels; that formula, with n lanes and wheelbase l, is the trap option. \(V/2R\) and \(nl^{2}/R\) are not standard forms.

Q: The minimum length of Transition Curves as per Indian Road Congress for plain terrain is:(Symbols have their usual meaning)

The IRC minimum length for plain terrain is \(2.7\ V^{2}/R\).IRC gives the minimum length of a transition curve from the empirical formula:\[ L_s = \frac{2.7\,V^{2}}{R} \]for plain and rolling terrain (and \(V^{2}/R\) for mountainous terrain), with V in km/h and R in metres; the design length is the larger of this and the lengths from the rate of change of centrifugal acceleration and the rate of introducing superelevation. \(0.0215\ V^{3}/CR\) is the centrifugal acceleration criterion, not the plain-terrain minimum, and the other two options are not IRC formulae.

The shift of the curve(all in meter units if 'L' is length of the long chord and 'R' is the radius of curve) is:-

A.\(L^{2}/R\)
B.\(L^{2}/24R\)
C.\(L^{2}/2R\)
D.\(L^{2}/6R\)

Exam Year(s)

RSMSSB JE - 2025, RSMSSB JE Agriculture - 2025, RSMSSB - 2025,

Answer: B

The shift is \(L^2/24R\).

When a transition curve is inserted, the circular curve has to be moved inward by the shift

\[ S = \frac{L^2}{24R} \]

where L is the length of the transition curve and R the radius of the circular curve. (The stem calls L the long chord.) \(L^2/6R\) is the offset at the end of the transition curve, four times the shift, and \(L^2/2R\) is the offset of a simple curve, so they are the usual traps.

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Psychological Widening in the extra width provided in the pavement on the curves is:
(symbols have their usual meaning)

A.V/2R
B.\(V/9.5\sqrt{R}\)
C.\(nl^{2}/2R\)
D.\(nl^{2}/R\)

Exam Year(s)

RSMSSB JE - 2025, RSMSSB - 2025,

Answer: B

Psychological widening is \(V/9.5\sqrt{R}\).

On curves, drivers tend to keep a greater clearance from the vehicle alongside, so IRC adds a psychological widening in metres:

\[ W_{ps} = \frac{V}{9.5\sqrt{R}} \]

with V in km/h and R in metres. The total extra width is this plus the mechanical widening \(nl^{2}/2R\), which allows for the rear wheels tracking inside the front wheels; that formula, with n lanes and wheelbase l, is the trap option. \(V/2R\) and \(nl^{2}/R\) are not standard forms.

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The minimum length of Transition Curves as per Indian Road Congress for plain terrain is:
(Symbols have their usual meaning)

A.\(0.0215\ V^{3}/ CR\)
B.80/ 75 + Y
C.\(2.7\ V^{2}/R\)
D.\(V^{2}/225\ R\)

Exam Year(s)

RSMSSB JE - 2025, RSMSSB - 2025,

Answer: C

The IRC minimum length for plain terrain is \(2.7\ V^{2}/R\).

IRC gives the minimum length of a transition curve from the empirical formula:

\[ L_s = \frac{2.7\,V^{2}}{R} \]

for plain and rolling terrain (and \(V^{2}/R\) for mountainous terrain), with V in km/h and R in metres; the design length is the larger of this and the lengths from the rate of change of centrifugal acceleration and the rate of introducing superelevation. \(0.0215\ V^{3}/CR\) is the centrifugal acceleration criterion, not the plain-terrain minimum, and the other two options are not IRC formulae.

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Horizontal Alignment and Superelevation Questions and Answers

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Horizontal Alignment and Superelevation Questions and Answers

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