At the interface between the earthwork subgrade and engineering structures, a change in railway track stiffness is typically observed. This section of the railway, which significantly affects the dynamic forces acting on the track and the interaction between the track and rolling stock, is referred to in technical literature as the track stiffness transition zone. In this zone, the interaction of the railway superstructure with the embankment section and the concrete foundation of engineering structures behaves differently under the dynamic loads imposed by passing trains. In railway design, appropriate measures must be considered to ensure a gradual change in stiffness in this area in order to maintain proper track performance and ensure the safe operation of trains. One such measure that can be implemented in the track superstructure is the installation of additional rails with a specified length between the two main rails, aimed at controlling differential settlements in this zone. In this study, the performance of additional rails installed in the railway superstructure at the entrance of Kouhin Tunnel on the Qazvin–Rasht railway line was evaluated through numerical modeling. The results of the analyses showed that using additional rails with a length of 18 meters reduces settlement in the ballasted section of the track by 16 percent. Another approach to reduce the vertical differential settlement between the two sections of the track is to decrease the stiffness of the track structure in the concrete section. This can be achieved by using an elastic layer, such as an elastic mat or pad, either beneath the rail or beneath the concrete track slab. The presence of such a mat reduces the stiffness of the track in the concrete section and increases track settlement, which helps bring the stiffness of the ballasted and concrete sections closer to each other.