Highway alignment planning: During the reconnaissance stage for a new highway project, which technique provides the most efficient broad-area coverage to identify feasible corridors before detailed surveys?

Introduction / Context:
Reconnaissance is the very first field step in highway alignment selection. The aim is to quickly scan large areas, shortlist feasible corridors, and flag major constraints such as steep terrain, rivers, protected forests, and built-up zones. Choosing the right reconnaissance method reduces cost and time for subsequent surveys.

Given Data / Assumptions:

• Objective: obtain a rapid overview of large terrain stretches.
• Output: candidate corridors for preliminary and detailed surveys.
• Constraints: cost, time, and need for wide coverage.

Concept / Approach:
Aerial photographic (or modern aerial/remote sensing) reconnaissance captures broad swaths of terrain efficiently. Orthophotos and photogrammetry allow quick interpretation of landforms, drainage, land use, and potential alignment obstacles. This method is superior to detailed ground-based surveys at the reconnaissance stage because it balances scale, coverage, and cost.

Step-by-Step Solution:
Clarify reconnaissance goal: screen large areas, not produce final staking details.Compare methods: aerial imagery offers fast, wide coverage with interpretable features.Select aerial photographic survey as best-suited for early-stage corridor identification.

Verification / Alternative check:
Highway manuals describe a progression: reconnaissance (aerial/desktop + field drive) → preliminary survey → detailed survey. Reconnaissance relies heavily on aerial/topo data to keep costs low and decisions informed.

Why Other Options Are Wrong:

• Cadastral surveys: focus on property lines; too detailed for initial corridor selection.
• Topographical ground surveys: essential later, but time-consuming for first screening.
• Triangulation surveys: geodetic accuracy task, not suited for fast reconnaissance screening.
• None: incorrect; aerial methods are clearly beneficial.

Common Pitfalls:

• Jumping straight to detailed ground surveys without broad screening increases costs.
• Ignoring seasonal imagery; wet-season photos can reveal drainage issues missed otherwise.

Final Answer:
Aerial photographic survey