In highway construction surveying, cross-sections for a road are typically taken at right angles to the centre line, at standard intervals (e.g., 30 m), at intermediate points where the gradient changes abruptly, and at the start-and-end points of curves. Which statement best captures this practice?

Introduction / Context:
For roadway earthwork estimation and geometric control, engineers take cross-sections of the proposed highway alignment at regular and critical locations. These cross-sections record ground levels, widths, and side slopes, enabling accurate quantity computation and design verification. Understanding where and how frequently to take sections is a core surveying skill in highway engineering.

Given Data / Assumptions:

• We are discussing field practices for setting out and measuring cross-sections along a highway centre line.
• Standard interval often used in plain terrain is about 30 m, subject to project specifications.
• Additional sections are needed at geometric or topographic changes.

Concept / Approach:
Cross-sections are generally set perpendicular (right angle) to the road centre line to correctly intersect the ground profile and reflect true widths and side-slope lengths. Regular spacing (such as 30 m) captures gradual terrain changes efficiently. However, terrain is seldom perfectly uniform; hence, extra sections are taken wherever abrupt grade breaks occur (crest/sag points, cut-fill transitions) and at the beginning and end of horizontal or vertical curves. This ensures the volume computations (by average end area or prismoidal methods) are accurate and the design intent is properly represented.

Step-by-Step Solution:
Identify the standard orientation: sections at right angles to the centre line → correct.Apply a regular spacing: e.g., every 30 m in fairly uniform ground → correct.Add intermediate sections: wherever the gradient or ground profile changes abruptly → correct.Include curve control: take sections at the start and end of curves to capture geometry → correct.Therefore, the inclusive choice is “All the above.”

Verification / Alternative check:
Highway survey manuals recommend denser spacing in undulating or rocky areas and at structures (culverts, bridges) to avoid under/over-estimation of earthwork. This aligns with the listed practice.

Why Other Options Are Wrong:

• Any single item alone is incomplete; robust practice requires all listed placements.

Common Pitfalls:
Using only fixed intervals regardless of terrain; failing to capture curve transitions; not taking sections perpendicular to the centre line, which leads to width and quantity errors.

Final Answer:
All the above.