Difficulty: Easy
Correct Answer: 6.7 m
Explanation:
Introduction / Context:
Two-lane National Highways are designed to accommodate opposing traffic safely at design speeds. The carriageway width must be sufficient for typical heavy vehicles with lateral clearance.
Given Data / Assumptions:
Concept / Approach:
Using a lane width of approximately 3.35 m per lane for two lanes gives a typical minimum carriageway width of 6.7 m. (Note: Some modern standards adopt 3.5 m lanes, giving 7.0 m, but the commonly cited minimum legacy value associated with 3.35 m lanes is 6.7 m.)
Step-by-Step Solution:
Verification / Alternative check:
Textbook cross-section tables list 6.7 m as a standard two-lane carriageway width where 3.35 m lanes are adopted; with 3.5 m lanes, the value becomes 7.0 m (beyond the given options).
Why Other Options Are Wrong:
4.7 m and 5.7 m are too narrow for safe two-way heavy-vehicle operation; 7.7–8.0 m exceed the typical minimum and would represent wider lanes or added paved shoulders.
Common Pitfalls:
Mixing up carriageway width with roadway or formation width; assuming paved shoulders are part of the stated carriageway.
Final Answer:
6.7 m
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