Recommendations

As for future research directions, methodological improvements could refer to several aspects of model refinements. First, pending upon data availability, additional contributing factors may be considered in model development, such as pavement design characteristics, detailed climatic information (average and peak temperatures, moisture etc), modal split of traffic etc. Second, for the case of survival analysis models, alternative distribution functions can be investigated and compared to the log-logistic functional forms. Third, for ANN, advanced, multi-layer structures could be considered, along with a detailed sensitivity analysis of the ANN. Indeed, the current ANN approach establishes the magnitude of effect each input has on the result, but future research should also provide insight on the type (positive/negative) and distribution (linear, non-linear, etc) of this effect.

Another aspect that future research can focus on is the potential transferability of the model. This implies testing alternative datasets (from other regions and countries) in an effort to

validate the models’ applicability to other areas of the globe. As indicated earlier, this would

also imply the incorporation of possibly additional explanatory parameters, which could aid both in a further improved representation of the underlying mechanism (in the case of duration models) and the forecasting performance of models developed.

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