When modelling road replacement projections, the major problem to be addressed is the estimation of economic life of roads and its projection into the future. Age is not taken into account when the decision is made to replace a specific road, as age in itself does not contribute to the costs or benefits of asset replacement. However age is an indicator of the probability of the need for asset replacement, it being more likely that an old road will need replacement compared to younger roads. A method is described which uses empirically derived age/roughness probability relationships as the basis for generating replacement projections. The age profile of the road network, and the proportion within each age group exceeding a specified roughness limit can be used to formulate this age/roughness probability relationship. This relationship can then be applied to the future by applying the age/roughness probability relationship to each subsequent future network age profile on a rolling five year cycle. The assumptions implicit in the model and the effect of different future scenarios on the projections for South Australian rural roads using the probabilistic model are discussed. (A)
Abstract