The objective of this research, undertaken in 2008–11, was the development of an improved method of modelling the decision to rehabilitate a typical New Zealand thin-surfaced unbound granular pavement. This was driven by previous research that had found a poor correlation between the recorded data and the decision to rehabilitate. It had been hoped that by talking to local engineers and examining pavements proposed for rehabilitation that distress not currently recorded might be identified. This would have then driven the development of better models and may also have expanded the detail collected in the visual surveys. The research found that the drivers are not obvious and that the decision may be based on factors other than those of an engineering nature.
It is recommended that a more consistent decision making process be developed that places more emphasis on the present pavement condition rather than the present emphasis on the net present value of future maintenance costs.