CBR method – why it is considered more accurate for flexible pavement design The California Bearing Ratio (CBR) method is considered more accurate primarily because it explicitly incorporates which key factor?

Introduction / Context:
The CBR method is a long-standing empirical approach to flexible pavement design. Its reliability in many contexts stems from how it links pavement thickness to measured support conditions.

Given Data / Assumptions:

• We are selecting the primary reason for improved accuracy.
• CBR values are measured on the subgrade and sometimes on sub-base/base materials.

Concept / Approach:
CBR design curves directly relate layer thickness requirements to the bearing capacity (CBR) of the supporting soil. While traffic category is also used to choose a design chart or traffic class, the essential accuracy improvement comes from basing thickness on measured soil strength rather than a generic soil type alone.

Step-by-Step Solution:
Obtain representative CBR of subgrade.Use traffic category to select appropriate design curve.Read required thicknesses from the curve which depends primarily on soil bearing capacity.

Verification / Alternative check:
Comparing two sites with identical traffic but different subgrades shows different thickness requirements, highlighting the soil characteristic dependence.

Why Other Options Are Wrong:

• Traffic intensity is considered, but it is not the core reason for the method’s improved accuracy; traffic affects the selection of curve, not the intrinsic thickness relation.
• Character of road-making materials influences layer coefficients in mechanistic-empirical methods, not the central CBR relation.
• 'None of these' is clearly incorrect.

Common Pitfalls:
Using soaked vs unsoaked CBR inconsistently; taking single-point CBR without variability checks; ignoring seasonal moisture effects.

Final Answer:
characteristics of soils