In geometric design of highways, a floating gradient is defined as the longitudinal grade on which a vehicle can maintain a specified speed without any tractive effort. What is this gradient called?

Introduction / Context:
Grades strongly influence vehicle performance. Designers consider several benchmark gradients to balance earthwork, cost, and operations (ruling, limiting, exceptional, and floating).

Given Data / Assumptions:

• Specified speed is maintained with zero net tractive effort.
• Resistances such as rolling and air resistance are balanced by gravity component.

Concept / Approach:
On the floating gradient, the downhill component of weight exactly balances resistances, so the driver neither accelerates nor applies power to maintain speed. It is relevant for fuel economy and safety on long downgrades.

Step-by-Step Solution:

Verification / Alternative check:
Vehicle performance charts show speed holding without throttle/brake at this gradient.

Why Other Options Are Wrong:
Ruling gradient is the desirable maximum design gradient; pushing gradient is a term used informally for steeper upgrades requiring extra tractive effort; minimum gradient is provided for drainage, not performance.

Common Pitfalls:
Confusing floating with ruling or limiting gradients; ignoring vehicle mass and resistance assumptions.

Final Answer:
Floating gradient