Condition for “no super-elevation” provision: A circular curve of radius R = 1400 m carries traffic at 80 km/h. If the practice is to omit super-elevation when camber alone is adequate, what camber (%) would satisfy this condition?

Introduction / Context:Super-elevation (e) and side friction (f) together balance the lateral acceleration on curves according to the relation e + f = V^2 / (225 R) when V is in km/h and R in metres. For gentle curves, practice sometimes omits super-elevation if the normal camber provides sufficient cross fall to meet the equilibrium condition comfortably.

Given Data / Assumptions:

• Design speed V = 80 km/h.
• Curve radius R = 1400 m.
• No super-elevation provided → e = 0; camber provides the cross slope.
• Check uses the equilibrium equality for threshold.

Concept / Approach:

Set e = 0 and compute the equilibrium value V^2 / (225 R). If the available camber equals or exceeds this value, super-elevation may be omitted. Typical bituminous road cambers are around 2% on straights, which may be adequate for very large-radius curves at moderate speeds.

Step-by-Step Solution:

Verification / Alternative check:

With camber 2%, the small remaining demand is within practical tolerance, especially considering conservative rounding and operational variability.

Why Other Options Are Wrong:

• 4%, 3%: Higher than necessary; super-elevation would certainly not be required, but these exceed typical straight-road cambers.
• 1.7% or 1%: Too small; would not satisfy the equilibrium threshold (~2.03%).

Common Pitfalls:

• Using the constant 127 from railway formulas; highway practice with friction uses 225 for km/h and metres.

Final Answer:

2%.