By Dr. Sachi Kodippily and Dr. Theuns Henning
Smart planning of infrastructure projects and maintenance of assets has a significant benefit to the entire community. Particularly in a country like New Zealand where population is sparsely distributed, having a well-planned and well-maintained road network is vital to ensuring safe and efficient movement of people and goods. Accurate long term planning of maintenance and management is a critical step to ensuring that our largest asset is performing in an appropriate condition for today and in the future.
Road condition prediction is an area of growing importance and plays a significant role in achieving asset management goals. Condition forecasting methods have much value as they provide an overall view of the asset conditions into the future, allowing for road asset valuations and determination of remaining service lives. This forecasting is also ideal when dealing with scenarios where varying funds may be available to achieve levels of service that are appropriate to the local area. There have been many different methods that have been developed over the years for forecasting road deterioration, with most of these methods utilizing deterministic or stochastic modeling techniques. A well-known and widely utilized example is the World Bank HDM-4 model, which is a versatile tool used for road condition prediction. In New Zealand, several road deterioration models have been developed which have used the HDM-4 model as a basis for producing area-specific models. Such models include continuous probability models for predicting typical performance trends of individual distresses, such as rutting or cracking. The models play an important role by reporting the current condition of the road asset as well as allow for prediction of future conditions, life cycle performance analysis and to assess the impact of alternative treatment strategies.
Figure 1: Deterministic model for predicting rutting
Figure 2: Stochastic model output
To gain the most out of the performance prediction analyses, the models need to have good geographical transferability and reliability for different application areas. A shortfall that is often encountered in many of the road maintenance planning decision tools is that they lack accuracy and robustness when used outside of the context, application area or time frame. Therefore in order to achieve consistency in investment analysis for any given time horizon, an appropriate analysis approach needs to be selected for optimum results. For short term planning, field decisions and project prioritization may be appropriate to deal with various maintenance situations, while longer terms require more specialized and accurate planning. Deterministic models can often provide a reliable measure of the condition of the assets for medium-term planning, and anything longer requires more full-picture type techniques, such as stochastic models. The dTIMS system is a useful strategic and tactical maintenance investment planning tool which has incorporated these many different types and forms of condition forecasting models. The benefit that dTIMS provides is that it allows for flexibility and accuracy in the modeling for any technique or time frame.
Figure 3: Maintenance forecasting horizons 1
The benefit to local road controlling authorities
For many local road controlling authorities, road asset deterioration and condition modeling is still a new concept, and many are still in the process of realizing the benefits that can be achieved. Often, the short-term decision making tools work on a snapshot of the condition of roads, but this may not necessarily ensure the best use of funds. Planning for longer terms is not often conducted by local authorities, and this makes it difficult to recognize its important and future benefits. But it is vital that all local road controlling authorities adopt 30-year planning strategies, and this is where dTIMS can help.
A standout feature that sets dTIMS apart from the other methods of planning is the degree of accuracy the tool can provide in predicting the future conditions of road assets. Short term planning is adequate for small projects, however for larger projects or assets that are valuable, precise long-term planning is essential. Many of the road assets that were developed in the 60s and 70s are now coming up for renewals, and this adds to the workload and stretch already tight budgets. There is a fine balance between attending to the urgent short-term maintenance needs of a road network, and at the same time plan well-ahead into the future to avoid an unexpected influx of maintenance work. Furthermore, it is not only important to know what the next treatment should be for a site, but it is also beneficial to identify the follow-on treatments based on today’s decisions and planning. Currently the only tool that can successfully achieve these objectives is the dTIMS system. With clear planning and a long term strategy, we can ensure efficient and satisfactory performance of our most important road infrastructure assets for many more years to come.