Highway gradients – where are “floating gradients” generally adopted? A floating gradient is the minimum downgrade at which a vehicle can continue at a constant speed without engine tractive effort. On an alignment, such gradients are generally provided:

Introduction / Context:
Gradient selection balances operating economy and safety. The “floating gradient” concept is useful on long rolling sections because it is the least downgrade where vehicles can coast at constant speed with engine idling, neither accelerating nor decelerating.

Given Data / Assumptions:

• Vehicles experience rolling and air resistance.
• On a small downgrade, component of weight along the slope offsets resistances.
• Floating gradient is typically small in magnitude (a minimum downgrade).

Concept / Approach:
Let resistances per unit weight be represented by coefficients. At the floating gradient, the downslope component W * sinθ equals the sum of resistances (rolling ± aerodynamic). With small θ, sinθ ≈ tanθ ≈ gradient. Hence the floating gradient is a minimum steady downgrade that sustains speed without throttle.

Step-by-Step Solution:

Verification / Alternative check:
On grades steeper than the floating value, vehicles tend to accelerate (needing brakes). On flatter grades, vehicles slow unless power is supplied, matching the floating concept.

Why Other Options Are Wrong:
Maximum gradients are steep and cause acceleration, not floating. Summit/valley curves describe vertical curve locations, not the gradient category. “Everywhere” is incorrect because floating gradients are specific downgrades, not universal.

Common Pitfalls:
Confusing floating gradient with ruling or exceptional gradients; ignoring aerodynamic drag at higher speeds which slightly raises the floating value.

Final Answer:
Along minimum gradients