The study sets out to investigate the use of rubber granules from used tires as solid (elastic) particles (without steel wires) mixed with conventional ballast aggregates for enhanced track performance (i.e., a rubber intermixed ballast stratum, or RIBS). The study evaluates the performance of RIBS subjected to both monotonic and cyclic loads by conducting large-scale triaxial tests for a range of rubber contents (0%–15%) under different confining pressures (10–60 kPa). It is evident from the results that rubber particles ranging from 9.5 to 19 mm with similar angularity to ballast aggregates are advantageous because they reduce the breakage of load-bearing larger aggregates, thus effectively controlling ballast fouling within the granular matrix while providing adequate resiliency. This project also demonstrated that particle densification at the conditioning phase can cause a reduction in permanent strains during the cyclic loads, thereby increasing track longevity.