Load Distribution Factor:

The formula for deriving at the number of repetitions of the standard axle load during a design period of n years is:

N =365 × A × VDF × F [(1 + r )ⁿ - 1]/r

where A = Number of commercial vehicles per day initially (both directions),

VDF = Vehicle Damage Factor,

F = Load Distribution Factor,

r = Annual rate of growth of traffic (in decimals), and

n =  Design period in years.

Thus, if a two lane road has a present commercial traffic of 4000 veh/day, and the design period is 15 years, the rate of growth of traffic is 7.5%, and the VDF is 3.5, the number of repetitions of standard axle loads during the design Period

N =365 × A × VDF × F [(1 + r )ⁿ - 1]/r

A = 4000

VDF = 3.5

F = 0.75 (Table 4.3)

r = 7.5% = 0.075

n = 15

Substituting, N = 365 × 4000 × .35 × 0.75 [1.07515 - 1]/0.075

= 365 × 4000 × 3.5 × 0.75 [2.96 - 1]/0.075

= 100 million

The million standard axles of repetitions is denoted by "msa".