IRC recommendation – extra widening for hill roads (curve radius = 150 m) According to Indian Roads Congress practice, the additional carriageway width (extra widening) to be provided on hill roads at a horizontal curve of radius 150 m is approximately:

Introduction / Context:
Vehicles require extra width on horizontal curves due to off-tracking and psychological clearance. On hill roads—where radii are often small and lane discipline is critical—IRC provides guidance for “extra widening.”

Given Data / Assumptions:

• Hill road with curve radius R = 150 m.
• Conventional design vehicle and lane width per IRC rural road standards.
• We seek the typical tabulated/derived extra widening.

Concept / Approach:
Extra widening W is the sum of mechanical widening (due to off-tracking) and psychological widening (driver comfort). For moderate radii around 150 m, the required extra width is modest but non-zero—commonly about 0.5 m per carriageway in practice for two-lane hill roads.

Step-by-Step Solution:
Recognize R = 150 m → moderate curvature.From standard practice/tables, select ≈ 0.5 m as typical extra width.Match the closest option → 0.5 m.

Verification / Alternative check:
Design tables using W = nl^2/(2R) + C (where n depends on lanes, l is wheelbase, C is psychological allowance) produce values near 0.5 m for this radius with typical parameters.

Why Other Options Are Wrong:

• 1.0–2.0 m: too large for R = 150 m under common lane widths and speeds.
• 0.0 m: underestimates need; vehicles do off-track on curves.

Common Pitfalls:
Applying plain-terrain extra widening criteria to hill roads or ignoring psychological component at small radii.

Final Answer:
0.5 m