Collisions constitute a primary contributor to bridge failures across navigable waterways, necessitating the implementation of crashworthy devices for damage mitigation. This investigation systematically examines the impact behavior of bridge protection systems with varying polyurethane fill ratios through horizontal impact testing. Experimental results reveal that polyurethane infill profoundly modulates both the peak magnitude and temporal evolution of impact forces. The deformation characteristics demonstrate significant fill ratio dependence, with lower filling percentages exhibiting enhanced nonlinear response under repeated impacts and reduced structural resilience. The failure mode of the device is also influenced by the polyurethane: without filling the outer steel plate undergoes buckling failure only after the second collision, reducing its energy absorption capacity. In contrast, polyurethane filling mitigates local buckling at the top of the steel plate, minimizing damage. However, at higher impact energy levels, buckling still occurs at the foot of the steel plate, eventually leading to failure. This study demonstrates that varying polyurethane fill ratios significantly influences the mechanical response and failure modes of crashworthy devices, offering insights into optimizing their design for bridge protection.