Design Traffic (N & msa)

Computes design traffic in standard axles (N and msa) using initial CVPD, growth rate, design life, lane distribution factor and vehicle damage factor.

1. Commercial traffic & growth

Traffic at count year, growth to opening year, and design life.
Average daily commercial vehicles at count year.
Use 0 if no growth is assumed.
If traffic is counted in opening year, set t0 = 0.
Typical flexible pavement design life 15–20 years.

2. Lane distribution & damage factor

e.g. 0.5 for 2-lane single carriageway, 0.75 for 4-lane, etc.
From axle load survey or code tables.

Design traffic in standard axles:
N = 365 · Aopening · [ ((1 + r)ⁿ − 1) / r ] · D · F
where Aopening = A0 · (1 + r)t₀. For r = 0, N = 365 · Aopening · n · D · F.