Correct : a

Option A — True
In horizontal curve design, IRC recommends a lateral friction coefficient of 0.15 (for high speeds) to prevent skidding while turning. For stopping sight distance computation, the longitudinal friction coefficient is much higher — around 0.35 to 0.40 — because braking friction along the direction of travel is greater than the lateral friction in a curve. The lower value is used in curve design to provide a comfortable, conservative margin of safety. A is true.
Option B — False
Centrifugal force on a horizontal curve is counteracted by superelevation — the entire carriageway is tilted so the outer edge is higher than the inner edge. This is not the same as raising the middle of the pavement. Raising the middle creates a camber/crown, which actually works against superelevation. B is false.
Option C — False
Grade compensation means reducing the ruling gradient on sharp horizontal curves to compensate for the additional resistance a vehicle experiences on a combined curve and grade. The gradient is decreased, not increased. If the curve is very sharp, the permissible gradient is reduced by the grade compensation amount. C is false.
Option D — False
For a bidirectional two-lane road, overtaking sight distance (OSD) governs summit curve design, and OSD is far larger than stopping sight distance (SSD). For a unidirectional road, only SSD is needed. So the bidirectional summit curve is longer, not shorter. D is false.
Correct answer: A ✓