Skid resistance is a vital issue in pavement management, mainly in relation to road safety; hence, road agencies must assure a minimum friction level of their road networks. The regional government of Biscay (Spain) uses a sideways force coefficient routine investigation machine to assess the present pavement surface condition and to allocate the available funding better. The aim of this paper is to develop a deterioration model to predict the minimum skid resistance in the rural two-lane bituminous roads of Biscay by means of the factors that affect it. In an attempt to include all possible variables that could influence the friction, 23 sections of new roads in Biscay, constructed over the last 25 years, were selected, with different pavement structures (flexible and semi-rigid pavements), ages, surface layers and traffic volumes; a multiple linear regression was then performed. It was concluded that only the average annual daily traffic of heavy vehicles and the required minimum polished stone value of aggregates reflect their importance and, consequently, they are the only variables introduced in the model. The age of pavement, total thickness of bituminous layers and average annual daily traffic of all vehicles showed no influence and were discarded. The proposed model can forecast future skid resistance.
