The lead of a crossing is measured as the distance starting from the__________________?
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Answer: B. heel of the switch to the theoretical nose of the crossing
Explanation
The lead of a crossing is measured horizontally from the heel of the switch to the theoretical nose. Theoretical nose represents the geometric intersection point of the gauge lines of the crossing. This standardized measurement defines the overall longitudinal layout length of a turnout assembly. Turnout layout dimensions include switch length, lead length, and crossing frog proportions. Theoretical and actual nose points differ because the frog nose is blunt for strength. Surveyors use lead distances to mark out turnout locations accurately during track construction.
Railway track installation crews rely on exact crossing lead measurements to align switches properly. Turnout design tables list lead lengths to simplify field layout for civil engineering personnel. Precise lead positioning prevents track buckling and ensures smooth transitions through junctions. Option A measures switch length between switch heel and toe rather than crossing lead. Option C measures from switch toe instead of switch heel to the theoretical frog nose. Option D uses the actual nose instead of the theoretical nose point for length measurement.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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