Definition of formation width in road design: “Width of formation” of a road refers to which dimension in embankment or cutting?

Introduction / Context:
Formation width is a foundational geometric parameter because it dictates earthwork quantities, side slopes, drainage placement, and right-of-way needs. Misinterpreting it can lead to under-designed platforms and unsafe edges.

Given Data / Assumptions:

• Standard two-lane or multi-lane road sections in embankment/cutting.
• Shoulders and side margins are part of the formed platform.

Concept / Approach:
The “formation” is the prepared top surface (platform) on which the pavement structure sits. Hence formation width includes carriageway plus shoulders and any specified margins—measured at the top of embankment (or equivalent in cutting), not just the paved portion.

Step-by-Step Solution:
Identify the formed platform location: top of embankment/cutting.Include all components forming the platform (carriageway + shoulders).Select the option that explicitly states the top formation width.

Verification / Alternative check:
Standard cross-sections in design manuals depict formation width as the total top width accommodating the pavement and shoulders before side slopes begin.

Why Other Options Are Wrong:

• Carriageway or pavement+shoulders alone omit margins and do not explicitly tie to the embankment’s top platform.
• Width at ground level varies with side slopes; not a design control dimension.

Common Pitfalls:

• Confusing paved width with formation width.
• Ignoring shoulder and safety margin needs when estimating formation.

Final Answer:
Width of the embankment (or cutting) at the top formation level (carriageway + shoulders, and margins as applicable)