Pavement Design (IRC method) – Design traffic in msa for a 2-lane single carriageway (15-year life) Two-way CVPD at opening = 2000; vehicle damage factor = 3.0; lane distribution factor = 0.75; annual growth = 7.5%. Compute cumulative standard axles (msa).

Introduction / Context:
IRC pavement design requires estimating cumulative standard axles (N) over the design life using initial traffic, growth rate, lane distribution, and vehicle damage factor (VDF). Correct interpretation of the distribution factors is critical to avoid under- or over-design.

Given Data / Assumptions:

• Two-way commercial vehicles at opening, P = 2000 CVPD.
• Lane distribution factor (design lane) = 0.75 for a 2-lane single carriageway.
• VDF = 3.0.
• Annual growth r = 7.5% for n = 15 years.

Concept / Approach:

Design traffic N (standard axles) is computed by N = 365 * A * F * [[(1 + r)^n − 1] / r], where A is the initial CVPD in the design lane, F is the vehicle damage factor. With the data provided, a common interpretation uses A = P * 0.75 for the design lane on a 2-lane single carriageway.

Step-by-Step Solution:

Verification / Alternative check:

Using the per-direction split (0.5) and a 0.75 lane factor would halve A; however, the presence of an explicit 0.75 design-lane factor in the problem statement indicates A is to be taken as P × 0.75, matching the given answer band.

Why Other Options Are Wrong:

22.6, 10.1, and 5.3 msa arise from misapplying growth or lane/directional factors.

Common Pitfalls:

Double-counting both directional and lane factors, or using monthly/annual traffic instead of daily CVPD in the IRC formula.

Final Answer:

42.9 × 10^6