The multiplier for converting the number of commercial vehicles of different axle load an axle configuration to the number of standard axle-load repetition is termed as vehicle damage factor (VDF).

VDF = Equivalent of standard axles / commercial vehicle

The vehicle damage factor depend upon the

1. Axle configuration

2. Axle loading

3. terrain

4. Type of road

And hence the vehicle damage factor varies with the axle configuration, type of load, axle loading, terrain from region to region.