Highway and railway design — which profile information is required for construction setting-out and earthwork computation?

Introduction / Context:
Setting out highways and railways requires accurate representations of the terrain and the designed alignment. Two complementary forms of profile information—longitudinal sections and cross sections—are indispensable for geometric design, earthwork estimation, drainage planning, and quantity measurement.

Given Data / Assumptions:

• Longitudinal section (L-section) follows the centerline (or reference line) of the alignment.
• Cross sections (C-sections) are taken at right angles to the alignment at specified intervals and at critical points.
• Earthworks (cut and fill) must be computed accurately for cost and scheduling.

Concept / Approach:

The L-section provides an elevation profile along the route, facilitating vertical alignment (gradients, vertical curves), sight distance checks, and drainage gradient design. Cross sections furnish transverse ground shapes and enable calculation of cut/fill areas for each station, which integrate over chainage to yield earthwork volumes. Together, they also assist in staking out formation widths, side slopes, ditches, and structures (culverts, retaining walls).

Step-by-Step Solution:

Verification / Alternative check:

Contract documents and standard specifications invariably require both L- and C-sections for design approval and payment measurement, confirming dual necessity.

Why Other Options Are Wrong:

L-section only — misses volumetric data across formation width.
C-sections only — lacks grade control and vertical curve design context.
None — contradicts basic practice in linear infrastructure projects.

Common Pitfalls:

Taking cross sections too widely spaced in variable terrain; failing to update L-section after alignment shifts.

Final Answer:

both longitudinal and cross sections are required