The growth of slab track construction in recent years is mainly due to its high stability performance and low deterioration rates when subjected to high-demand railway traffic. Nevertheless, when required, slab track maintenance, such as track geometry correction, can be extensively expensive, time consuming and may involve rail service interruptions. Therefore, the development of tools that are able to analyse the performance and predict the behaviour of slab tracks over time can bring significant economic benefits to the railway industry. This work presents slab track settlement studies using a novel hybrid 3D finite-element tool (HI-Track), which is coupled with mechanistic empirical design, that is able to analyse the track behaviour over millions of train passages. The paper presents a case study of long-term experimental measurements conducted in a full scale test rig using the Bögl slab track system subjected to over 3 million load cycles emulating train operation over a long period of time. The HI-Track tool is used to investigate the long-term performance of the slab track laboratory test case, where simulations are compared and checked in a validation process. The main findings substantiate the reliability of the numerical tool to accurately predict track settlement within specified soil compressive strength of 70–100 kPa and a soil stiffness ranging between 100 and 400 MPa.