Large repetitive wheel loads from heavy haul and passenger trains can cause significant track deformation that leads to poor track geometry and safety issues. The inclusion of geosynthetics and rubber mats (i.e., shockmat) in critical sections in the track for reducing these adverse effects was further examined through an extensive field trial in the town of Singleton, New South Wales (NSW), Australia. Four types of geosynthetics and a shockmat were installed below the ballast layer in selected sections of track constructed on three different subgrades (soft alluvial clay, hard rock, and concrete bridge), and the performance of the instrumented track was monitored for five years under in-service conditions including tamping operations. The measured stress-deformation response indicates that the geosynthetics effec- tively control the long-term and transient strains in the ballast layer, with the obvious benefit of reducing maintenance costs. The study also showed that the aperture size of geogrids in the range of 1.1 times the mean particle size of the ballast was most effective. The placement of shockmat on a concrete bridge contributed to reduced ballast breakage. The dynamic amplification of stresses induced by moving trains was observed, and it became more pronounced at higher axle loads and train speeds. The dynamic track modulus was evaluated adopting the concept of modified beam on an elastic foundation (BOEF), and this approach was found to be largely influenced by the axle load, train speed, placement of synthetic inclusions, and type of subgrade.