Traffic and environmental conditions are key parameters in road applications. Empirical studies and numerical analyses, which are widely adopted in material design studies, are used for analysing superstructures of the roads, and developmental approaches are improved for future designs as well. In flexible pavements, polymer and fibre-reinforced additives are frequently used to make them durable against deteriorations and to extend their service life. One of the additives that is mostly preferred is the Styrene Butadiene Styrene (SBS) material thanks to a variety of their physical and chemical properties. Physical and mechanical properties of the natural ground layer and its interactions with the superstructure are crucial parameters in terms of performance under various environmental and traffic conditions. In this study, the use of SBS-modified Hot Mix Asphalt (HMA) was examined as a flexible superstructure, and the mechanical properties of the granular base and the natural ground layer were tested. The stress and deformation occurring within layers in various periods were also considered. The presented study is a suitable tool for the use of additives that significantly contribute to the mechanical properties and service life of the roads. In this study, it is concluded that the use of additives significantly improves the mechanical response and service life of the roads.