Distribution of extra widening on curves Where should the full amount of extra pavement width on a horizontal curve be achieved along a layout with transition curves?
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ABeginning of the transition curve
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BCentre of the transition curve
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CBeginning of the circular curve
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DCentre of the circular curve.
Answer
Correct Answer: Centre of the circular curve.
Explanation
Introduction / Context:Extra widening on curves is provided to accommodate off-tracking of long vehicles and lateral clearance at speed. On alignments with transition curves, the widening must vary smoothly.
Given Data / Assumptions:
- Curve layout includes transitions leading into and out of the circular arc.
- Extra width is linearly developed along transitions.
- Full extra width is needed over the tightest curvature (circular arc).
Concept / Approach:Because the radius is smallest on the circular arc, that is where the greatest off-tracking and lateral clearance demand occur. The widening should be zero at tangent, increase along transitions, and reach the full value at the middle of the circular arc for a symmetric layout.
Step-by-Step Solution:
Define linear widening distribution along each transition.At the end of transition (start of circular arc), widening reaches 50% of the full amount.At the centre of the circular arc, full widening is realized.Verification / Alternative check:Standard curve widening diagrams show triangular widening ramps on transitions peaking at mid-arc; this ensures comfort and uniform lateral clearance.
Why Other Options Are Wrong:Beginning or centre of transition provides only partial widening; beginning of circular curve captures only half of the requirement.
Common Pitfalls:Applying full widening abruptly at the start of transition; ignoring symmetry when different transition lengths exist.
Final Answer:Centre of the circular curve.