Railway transition zones between open track and rigid structures such as bridges and culverts often experience differential movements due to abrupt changes in track stiffness and complicated dynamic loading effects. Such conditions commonly lead to track geometry issues, consequently increasing the magnitude of impact loads at these areas. This in turn leads to excessive degradation of ballast and other track components. Under-ballast mats have seen increased use in the last decades especially in the area of improved vibration mitigation and track stiffness reduction at bridge approaches due to their flexibility and damping capabilities. This paperpresents results from an ongoing laboratory study aimed at investigating the effectiveness of under-ballast mats on the transient deformation behavior of track sections built over stiff substructures such as bridge decks and subjected to cyclic loading. According to the study findings, under-ballast mats can provide the necessary resiliency enhancements to track structure to mitigate differential settlements at transition zones by matching the vertical transient deformations of open track with those obtained over stiff support conditions.