•Unprecedented effects of unconstrained length of railway tracks are highlighted.•Physical nature of track buckling is studied using nonlinear FEM models.•Interspersed approach can shift failure from progressive to snap-through buckling.•Buckling of timber sleepered tracks can be prevented by interspersed approach.•Track lateral resistance plays a significant role in track buckling prevention. In a conventional railway system, timber sleepers have been widely used for ballasted railway tracks to carry passengers and transport goods. However, due to the limited availability of reliable and high-quality timbers, and restrictions on deforestation, the “interspersed” approach is adopted to replace ageing timbers with concrete sleepers. The replacement of ageing timber sleepers is frequently done over old and soft existing formations, which have been in service for so long, by installing new stiff concrete sleepers in their place. This method provides a cost-effective and quick solution for the second and third track classes to maintain track quality. Presently, railway track buckling, caused by extreme temperature, is a serious issue that causes a huge loss of assets in railway systems. The increase in rail temperature can induce a compression force in the continuous welded rail (CWR) and this may cause track buckling when the compression force reaches the buckling strength. According to the buckling evidences seen around the world, buckling usually occurs in ballasted track with timber sleepers and thus there is a clear need to improve the buckling resistance of railway tracks. However, the buckling of interspersed tracks has not been fully studied. This unprecedented study highlights 3D finite element modelling of interspersed railway tracks subjected to temperature change. The effect of the boundary conditions on the buckling shape is investigated. The results show that the interspersed approach may reduce the likelihood of track buckling. The results can be used to predict the buckling temperature and to inspect the conditions of interspersed railway tracks. The new findings highlight the buckling phenomena of interspersed railway tracks, which are usually adopted during railway transformations from timber to concrete sleepered tracks in real-life practices globally. The insight into interspersed railway tracks derived from this study will underpin the life cycle design, maintenance, and construction strategies related to the use of concrete sleepers as spot replacement sleepers in ageing railway track systems.