Thaw-weakening forecasting model for unpaved roads – An assessment, critical review, and development strategy

Northern conditions cause challenges to the trafficability of unpaved roads. In spring, melting ice and snow softens road structures causing thaw weakening. Unpaved roads play a significant role in everyday life, forestry and agriculture. For this reason, the Finnish Transport Infrastructure Agency uses a dedicated model to predict thaw weakening of unpaved roads. The current model forecasts the severity of thaw weakening of the upcoming spring, thus helping the road professionals and users to prepare and to avoid potential structural damage. The forecasting model was originally developed by the University of Oulu in 2004, assigned then by the Finnish Transport Agency. The model has been used for over 20 years now, and significant challenges regarding its validity have been identified. This study examines the specification and application of the current forecasting model. The study applies empirical analysis to compare forecasted and actual thaw weaking of unpaved roads. Comparative analysis is supplemented by interviews of practitioners. The results show that the current model significantly overestimates the severity of thaw weakening. Also, the validity of the model parameters must be re-evaluated, and the inclusion of new parameters should be considered. Moreover, the initial forecasting model does not apply to the current climatological conditions. As a conclusion, the study presents three strategies to develop the model: i) development of a completely new model, ii) development of an improved model relying partly on existing parameters and model architecture, iii) application of machine learning techniques to the improved model. The paper concludes that options ii) and iii) are the most feasible options to upgrade and improve thaw-weakening forecasting of unpaved roads.