Recommended camber for straight roads with water-bound macadam (WBM) or gravel surface: choose the desirable range.

Introduction / Context:
Camber ensures quick surface drainage, which is particularly critical for WBM and gravel surfaces that are more water-sensitive than cement concrete.

Given Data / Assumptions:

• Surface type: WBM or gravel.
• Straight road segments (no added superelevation).
• Climate not otherwise specified; choose a conventional desirable range.

Concept / Approach:
For permeable or less bound surfaces, a slightly steeper camber is recommended than for dense bituminous or concrete surfaces. Typical ranges lie around 2.5% to 3%, i.e., about 1 in 40 to 1 in 33.

Step-by-Step Solution:

Verification / Alternative check:
Field performance and standard camber tables for different surfaces corroborate this range.

Why Other Options Are Wrong:
1 in 33 to 1 in 25 (≈ 3 to 4%) is on the steeper side and may be excessive; 1 in 150 to 1 in 140 and 1 in 160 to 1 in 140 are far too mild for WBM/gravel and are typical of CC surfaces.

Common Pitfalls:
Using a “one value fits all” camber irrespective of surface type; ignoring erosion risk with very steep crossfall.

Final Answer:
1 in 40 to 1 in 33