The model uses 4 vehicle classes – Cars, Medium Commercial Vehicles, Heavy Commercial Vehicles and Super Heavy Commercial Vehicles. These classes are commonly used by models because they clearly delineate between vehicles with different operational characteristics. Each of these classes have different vehicle operating cost assumptions, different speed profiles and different propensity to cause congestion.
The usual basis for vehicle classification is the Austroads vehicle classification scheme, as shown in the figure below.
These classifications are broadly functional, in that similarly classified vehicles will have broadly similar operational characteristics. Due to the ubiquity of this classification (most traffic counts are reported as groupings of these classes) the model has used it as its basis for vehicles classes. Instead of the full 12-bin grouping we have adopted a 4-bin approach: Cars (Classes 1-2), Medium Commercial Vehicles (Classes 3-5), Heavy Commercial Vehicles (Classes 6-9) and Super Heavy Commercial Vehicles (Classes 10-12).