State highways carry large traffic volumes over long periods and through varying climatic conditions. Their strength comes from a layer of carefully graded and compacted stone immediately below the surfacing, called the 'base course layer'. This layer is supported by varying thicknesses of compacted gravel on top of the natural ground.
There are many considerations that go into selecting the right pavement type for a road.
These areas all need to be balanced through careful selection of the available options. The majority of our highways use a good-quality crushed local stone (aggregate) with a chip seal surface (layer of bitumen covered by stone chip). In areas that are more heavily trafficked we often use an asphaltic concrete (stones mixed with bitumen) to provide a better performance and level of comfort.
The volume of traffic on our highways means the pavements do deteriorate with time and sometimes need re-strengthening. How often depends on the road, but they typically last for between 20 and 50 years. We usually recycle the existing base course layer with additional new material.
Research undertaken by the CAPTIF Road Research Centre has significantly improved our pavement maintenance over recent years.
Find out how we monitor pavement condition.
