Abstract: Glass Fiber Reinforced Polymer (GFRP) composites are widely used in protective engineering for transportation infrastructure due to their advantages of lightweight, high strength, and corrosion resistance. Due to the high cost of full-scale vehicle impact tests, finite element (FE) simulation of contact collision has become an essential tool for evaluating the protective performance of anti-collision devices. To accurately assess the impact mitigation performance of such protective systems, this study conducted horizontal impact tests on GFRP flexible guard panels. Numerical simulation verification was carried out. The validated FE model was employed to evaluate the crash resistance of a full-scale composite protective device for an urban rail transit bridge pier. The results demonstrate that the proposed flexible guard panel significantly reduces the impact force and lateral displacement of the pier, with the maximum reduction rate of 87%, which can provide effective protection. For collisions involving different vehicle types, impact angles, and velocities, the energy dissipation performance remains highly stable, with the peak force reduction rates reaching 60%-80%. The protective performance is notably superior to that of existing rigid anti-collision devices. The findings of this study can serve as a reference for evaluating the low-velocity impact performance of similar structures.