This paper presents a theoretical viscoelastic approach, called PEDRO(PErmanent Deformation of asphalt concrete layers for ROads), for predicting rut formation in asphalt concrete materials subjected to traffic loading. Input data are traffic parameters, asphalt concrete viscosity and asphalt layer thickness. Vertical strains that cause rutting in the pavement were estimated using the PEDRO approach. A large-size type of wheel tracking machine, which has the capability to subject asphalt concrete slabs to different loadings has been used to study the effects of wheel load and tyre pressure. Rut development in the slabs under various loading conditions was predicted. The approach has shown reasonable results as regards predicting densification and shear rutting in tested asphaltconcrete slabs.