The roading industry in New Zealand has faced many challenges in recent times with reductions to funding budgets for road maintenance projects. This has put immense pressure on road controlling authorities and roading practitioners to use sound judgment and engineering wisdom to employ processes that will deliver savings not only in the short-term but also ensure that the financial status and condition of road networks in the future are not compromised. Classically, when it comes to maintenance of our road networks, the decision making process that was involved in selecting maintenance treatments for a set of roading projects has used a prioritisation process. The projects were ranked and sites that were in the worst condition were given priority in terms of funding, and maintenance was conducted until the funding pool was expended. This process simply took into account the current condition of a road site, but it did not consider the wider issues of road deterioration rates or the long-term impact of failure of a site.
The decision making process for maintenance planning for a particular road network needed to ensure that when maintenance projects were conducted, the sites that were most in-need of treatment in the short term were treated promptly, while concurrently being aware of the long-term impacts of such maintenance. Prioritising maintenance needs of a road network based simply on its current condition failed to show the long-term impact of the maintenance. The maintenance funding allocation process needed to include forecasts of the future conditions of a road network, however there was always the pressing issue of how to achieve accurate forecasts.
To achieve a balance between maintenance needs and budget constraints it was recommended that the process of project prioritisation was combined with budget optimisation. Optimisation is the process that is used to make a design or decision-making system efficient by maximising productivity or minimising waste, specifically, achieving the “best value” for the system based on a set of constraints. In the context of road asset management, the various maintenance options need to be analysed for their desired outcomes while taking into account constraints such as available budget or risk.
The use of the optimised maintenance project selection process ensured that when maintenance was conducted it was targeted to areas that would otherwise be the costliest if failure occurred, while at the same time ensuring the timing of the maintenance was perfect. This method of optimised maintenance planning, as opposed to site-specific treatments, achieved an overall better network condition as well as significant monetary savings.
The NZ dTIMS system was recommended as a tool to conduct performance forecasts for selecting the sites that were most in-need of maintenance. The ease in which the NZ dTIMS system could be aligned to each road network allowed it to be effective in the optimisation process.
When the forecasts from NZ dTIMS were used, it was found that the routine maintenance costs for a particular road network was dramatically reduced, while at the same time the road condition was maximised. The NZ dTIMS system was shown to be an ideal planning tool for periods of 10 to 20 years, given its strength in accurate forecasting of maintenance needs of a roading system. For a planning period of 10 years, the optimised maintenance program using the dTIMS forecasts achieved an overall better performance of the entire road network and a 10% reduction in the overall routine maintenance costs. This forecasting robustness of the dTIMS has confirmed the confidence in this system for planning and optimisation of maintenance spending for the New Zealand roading industry.