Candidate Selection Algorithm

The Candidate Selection Algorithm (CSA) is a significant advancement in the way New Zealand’s roading sector identifies surface and pavement renewal work.

An evolution of the original Treatment Selection Algorithm (TSA) from the 1980s, the CSA incorporates decades of industry learning, updated asset management practices and the latest in condition data collection.

Its primary function is to help Road Controlling Authorities (RCAs) identify candidate sites for renewal interventions - such as resurfacing or rehabilitation - over their planning cycles.

Benefits

The CSA provides substantial benefits by:

• Enabling a consistent approach to identifying sections of road that may need surface or pavement renewal.
• Supporting the development of forward works programmes that are better aligned with actual network needs.
• Improving the consistent and efficiency of planning across RCAs, ensuring continuity as industry standards evolve.
• Fostering greater confidence and ongoing collaboration to further refine the tool.

Development

In 2020 REG funded the development of the CSA by the Roading Infrastructure Management Support Group (RIMS). It involved several stages:

1. Developing a digital prototype based on improvements identified in NZTA’s research.
2. Coding and testing the algorithm within dTIMS; and
3. Validating its outputs against real-world forward works programmes (FWPs) in Auckland.

The validation process included both desktop and field analyses, comparing the CSA’s recommendations with actual field-validated FWPs and refining the algorithm based on observed ‘hit’ and ‘miss’ rates. The CSA had a higher success rate in predicting required treatments compared to the TSA.

The enhanced REG CSA will integrate the Consistent Condition Data Collection (CCDC) surveys for sealed roads and Asset Management Data Standard (AMDS) data. By using high-quality, standardised data from these sources, the enhanced CSA can provide evidence-based, consistent and transparent recommendations for surface and pavement renewal treatments. REG is testing and optimising the algorithm on real roads to evaluate its accuracy using the CCDC data.

Release plan

The CSA will be available via Transport Insights from early 2026. After receipt of the CCDC Year 2 data, RCAs will be able to use the CSA to develop their 2027-30 forward works programmes, 2027-2037 activity management planning and National Land Transport Programme bid.