Traffic loading

The traffic loading on concrete pavements should be consistent with the expected use of the pavement.  This webpage only covers road and highway pavements.

Austroads defines traffic loading into 12 classes as shown in Figure 1.

Figure 1: Description of the twelve vehicles classes in the Austroads pavement design guide
(Source: Austroads Pavement Design Guide, Part 2).

In the Austroads design guide the data required to determine the cumulative heavy vehicles over the design life are:

• Design traffic life in years (typically 40 years for highway pavements)
• The Average Annual Daily Traffic (AADT)
• The percentage of heavy vehicles in the daily traffic
• Heavy vehicle annual growth (may not be linear for the design life)
• Percentage of heavy traffic in the design lane or sometimes referred to as channelisation varying from 30 to 100%.
• The axle group loading distribution (that is the estimated percentage of axle group loads in kN for each of the 6 types of axle groups (see Figure 2)

Figure 2:  The six different axle group load configurations in the Austroads pavement design guide

The Austroads design guide provides two representative axle group distribution for rural and urban sites, and Figure 3 shows a representative axle load distribution used in highway concrete pavement design.  The sum of the axle group proportions must equal 1 and for each axle group proportion (vertical columns) must equal 100%.  For new pavement designs, the road agency usually provides the axle group load distribution.

Figure 3  A sample axle group distribution table and group proportions

In some situations, the location of the dual tyres location on an axle is needed for joint layouts of multilane carriageways.  While there is no definitive location and tyre widths vary, the dimensions in Figure 4 are representative of Australian highway vehicles.

Figure 4: Nominal location and width of the tyres for a dual tyre axle configuration.

Super-single tyres are not common in Australia and are typically found on fluid tankers as shown in Figure 5.  Given that the proportion of thee axle configurations are low and the overall location of the axle group load is important, super-single tyres are not considered different to a dual tyre in a tandem axle group loading (TADT).

Figure 5:  View of super single tyre on a triaxle group configuration