Shoulder drainage – minimum crossfall requirement What is the typical minimum crossfall (transverse slope) provided on highway shoulders to ensure positive drainage?

Introduction / Context:
Shoulders play a critical role in pavement edge support and surface drainage. Without adequate crossfall, water ponds at pavement edges, increasing moisture damage and reducing safety.

Given Data / Assumptions:

• Paved or earthen shoulders are contiguous with the main carriageway.
• Objective is to ensure runoff without excessive slope that may be uncomfortable or erodible.

Concept / Approach:
Design guides recommend a minimum transverse slope for shoulders typically around 2.5% to provide reliable drainage while maintaining stability and comfort. Steeper slopes may be used for unsealed shoulders based on soil and rainfall, but a minimum of 2.5% is a widely adopted baseline.

Step-by-Step Solution:
Identify the drainage need → avoid edge ponding.Adopt standard minimum → 2.5% crossfall on shoulders.Increase only if local conditions (soil/erosion) warrant it.

Verification / Alternative check:
Typical sections in design manuals show shoulder slopes equal to or slightly steeper than the camber of adjacent lanes, with a common minimum of 2.5%.

Why Other Options Are Wrong:
0.5–1.5% may be insufficient to drain during heavy rain; 3% can be acceptable but is not the baseline minimum—2.5% is the conventional lower bound.

Common Pitfalls:
Using too flat a slope near sag locations; neglecting erosion control when increasing slope on unsealed shoulders.

Final Answer:
2.5%