Rail freight plays a central role in sustainable mobility due to its lower emissions per ton-kilometer compared to road transport. However, improving braking safety and reducing maintenance costs remain essential to increase competitiveness. In this context, the implementation of Wheel Slide Protection (WSP) systems on freight wagons represents a promising upgrade, particularly with the forthcoming Digital Automatic Coupling (DAC), which will enable onboard power and data availability. In freight vehicles, the braking system is entirely pneumatic and the braking forces are applied directly to the wheel tread through brake blocks. Under degraded adhesion conditions, wheels may lock and slide, generating wheel flats that increase impact loads, accelerate fatigue of wheelsets and infrastructure, and significantly reduce braking performance. While WSP systems are widely adopted in passenger trains, freight wagons have not yet integrated this technology. This research investigates the retrofit of a WSP system on articulated freight wagons with minimal modifications to the existing pneumatic braking architecture. A high-fidelity numerical model is developed in MATLAB-Simulink, integrating vehicle dynamics, pneumatic circuit behavior, and a wheel-rail contact formulation capable of reproducing degraded adhesion and variable track conditions. The model supports the design of a control strategy that estimates longitudinal velocity and modulates brake cylinder pressure in real time through electro-pneumatic valves to prevent wheel lock-up. A central contribution of this work is the development of a dedicated Hardware-in-the-Loop (HIL) test bench for experimental validation. The platform combines real pneumatic components, electro-pneumatic valves, and embedded control hardware with a real-time simulation of vehicle dynamics and wheel-rail interaction. This configuration enables controlled and repeatable reproduction of braking events under degraded adhesion conditions while preserving realistic pressure dynamics. Experimental results demonstrate effective prevention of wheel locking, reduction of stopping distance, and maintenance of auxiliary reservoir pressure, confirming the robustness and practical feasibility of WSP implementation in freight applications.