Railway sleepers frequently deteriorate under the resonance effect, and modal parameters of sleepers are vital in avoiding or reducing such damage. Interestingly, the triaxial modal performance of concrete railway sleepers has yet to be investigated in the available literature. This study sheds light on this important literature gap. In this context, some of the lesser-known characteristics of prestressed concrete railway sleepers that affect modal performance are described in the study. In addition, several alternative sleeper models using carbon fiber reinforced polyurethane (CFRPU) laminate reinforcements and eco-friendly cement types were investigated comparatively with conventional prestressed ones. According to the full scale (triaxial) comparative experimental modal analysis (EMA) results, alternative sleeper models reached 75%, 94%, and 43% higher viscous damping ratios in the vertical, lateral, and longitudinal axis, respectively. Another important inference relates to the common trapezoidal-shaped, tapering-to-the-center geometry commonly used with mono-block sleepers. Triaxial comparative modal analysis allowed a preliminary investigation of the potential drawbacks of this particular geometry, such as a reduction in damping ratios in the lateral axis compared to the vertical.