Question

Which of the following statements is/are TRUE in the context of the geometric design of highways?

• A. The coefficient of friction used for the design of horizontal curves is lower than the coefficient of friction used in the computation of the sight distances.
• B. Centrifugal force at horizontal curve is counteracted by raising the middle of the pavement with respect to the edges.
• C. Grade compensation is achieved by increasing the gradient of the horizontal curve.
• D. Under identical conditions, the design length of the summit curve of a road having unidirectional flow will be greater than that of the same road having bidirectional flow.

Hint:

Check design friction values, camber vs superelevation, the direction of grade compensation, and how sight distance sets summit curve length for one-way vs two-way roads.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept.
This question checks several separate ideas from highway geometric design: friction values used in design, superelevation versus camber, grade compensation on curves, and sight-distance-based summit curve length for one-way versus two-way roads. Each option needs to be checked on its own against standard design practice.

Step 2: Key Formula or Approach.
Design friction values are not single fixed numbers: a lower design value of side (lateral) friction, about \(0.15\), is used for horizontal curve design, while a higher, speed-dependent design value of longitudinal friction, roughly \(0.35\) to \(0.40\), is used for stopping (braking) sight distance. Superelevation is the raising of the outer edge of the pavement relative to the inner edge on a curve; camber (crown) is the raising of the centre of the pavement relative to the edges, done for drainage, not for resisting centrifugal force. Grade compensation reduces the gradient at a horizontal curve to offset the extra resistance a vehicle feels while turning. Summit curve length is set by the required sight distance, and that requirement differs between one-way and two-way roads.

Step 3: Detailed Explanation.
(A) The friction value used for horizontal curve design (lateral/side friction, about 0.15) is lower than the friction value used for computing stopping sight distance (longitudinal friction, about 0.35 to 0.40). This matches the design values above, so (A) is TRUE.
(B) The statement describes raising the middle of the pavement relative to the edges, which is the definition of camber, provided for surface drainage. Centrifugal force at a curve is actually resisted by superelevation, which raises the outer edge relative to the inner edge, not the middle relative to the edges. So (B) is FALSE.
(C) Grade compensation is applied by reducing (easing) the gradient on a horizontal curve, not by increasing it, because a vehicle negotiating a curve already faces extra resistance from turning, and adding a steeper gradient on top of that would overload it further. So (C) is FALSE.
(D) On an undivided, two-way (bidirectional) road, a driver must often see far enough to overtake safely, or at least see an oncoming vehicle, which calls for a longer sight distance than the simple stopping sight distance needed on a one-way (unidirectional) road. A larger required sight distance needs a longer summit curve for the same deviation angle, so the bidirectional road tends to need the equal or longer curve, not the unidirectional one as the statement claims. So (D) is FALSE.

Step 4: Final Answer.
Only statement (A) is true.
\[ \boxed{\text{Option (A)}} \]