Highway engineering — standard single-lane carriageway width What is the recommended width of carriageway for a single-lane roadway as per common Indian highway design practice?

Introduction / Context:Carriageway width standards ensure sufficient lateral clearance for vehicle envelopes, steering wander, and safety margins. For single-lane roads, the carriageway must comfortably accommodate one design vehicle with allowances for mirrors and minor weave while minimizing construction cost.

Given Data / Assumptions:

• Design vehicle corresponds to standard Indian practice for rural single-lane roads.
• Shoulders are provided separately and are not included in the carriageway width.
• Normal traffic mix; not a special corridor for oversize vehicles.

Concept / Approach:Indian Roads Congress (IRC) recommendations specify carriageway widths by the number of lanes. A single-lane road has one traffic lane; two-lane two-way roads typically provide 7.0 m (two lanes of 3.5 m each), while a single lane is roughly half that plus a small allowance, commonly standardized as 3.75 m. Shoulders provide additional recovery space and passing opportunities at designated bays.

Step-by-Step Solution:Recall typical lane widths: multilane roads commonly adopt 3.5–3.75 m per lane.For a single-lane carriageway, use the standard single-lane width: 3.75 m.Select option 3.75 m.

Verification / Alternative check:IRC geometric design guidelines list 3.75 m as the carriageway width for single-lane roads, with shoulders specified separately depending on terrain and classification.

Why Other Options Are Wrong:7.5 m and 7.0 m: Correspond to two-lane roads.
5.5 m: Often associated with intermediate-width two-lane roads, not single-lane.
4.75 m: Wider than standard for single-lane and not typical in practice.

Common Pitfalls:

• Confusing carriageway width with roadway (carriageway + shoulders).
• Assuming urban curb-to-curb values apply to rural standards.

Final Answer:3.75 m