Camber selection on straight roads: For a straight road with a thin bituminous surfacing (surface dressing/OGPC type), what is the desirable camber range to ensure adequate drainage without causing discomfort?

Introduction / Context:Camber (cross fall) is provided on pavements to quickly drain surface water and protect the bituminous layer against moisture damage. The desirable camber depends on the surface type; bituminous surfaces require moderate camber that balances drainage with ride comfort and vehicle stability.

Given Data / Assumptions:

• Pavement surface: thin bituminous surfacing (e.g., surface dressing/OGPC).
• Road is straight (no super-elevation effects).
• Standard IRC practice for camber selection.

Concept / Approach:

Typical IRC-style guidance suggests: Earth roads ≈ 1 in 33 to 1 in 25; gravel/WBM ≈ 1 in 50 to 1 in 33; bituminous surfaces ≈ about 1 in 60 to 1 in 50; cement concrete ≈ about 1 in 60. Since the question specifies thin bituminous surfacing, the desirable camber is about 1 in 60 to 1 in 50—not any of the ranges listed in options (a)–(d).

Step-by-Step Reasoning:

Verification / Alternative check:

Design tables for camber corroborate that bituminous surfaces generally use ≈ 1 in 60 to 1 in 50. Local climate and rainfall intensity may cause minor adjustments but do not align with the options given.

Why Other Options Are Wrong:

• (a) and (b): Suitable for earth/gravel/WBM, steeper than needed for bituminous surfaces.
• (c) and (d): Excessively flat, risking water ponding on bituminous surfaces.

Common Pitfalls:

• Using earth-road camber values for bituminous pavements, which can reduce comfort and create edge erosion.
• Choosing very flat cambers that allow water to stagnate on the surface.

Final Answer:

None of these.