Clearance of bridge span is generally measured from which reference to the undersurface of the bridge?

• A. Span Length
• B. Clearance of bridge span
• C. Deck Width
• D. Clearance above bridge floor

Answer: (B)

Vertical clearance is about the space below the bridge, defined relative to a fixed reference plane (like the water surface or ground level) and measured up to the underside of the bridge. The quantity you’re describing—how much room exists beneath the span—depends on that reference datum, not on horizontal dimensions of the bridge. The option that matches this idea is the clearance of the bridge span, because it names the vertical space with respect to the chosen reference plane. The other options refer to horizontal dimensions (span length, deck width) or to a measurement that would be taken above the deck rather than below it (clearance above the bridge floor), which aren’t what’s being asked.