Yaw dampers are equipped on rail vehicles to prevent the arising of hunting motion at high-speed running. Nevertheless, standard devices must respect a design tradeoff due to their detrimental action on the curving performances of the vehicle. In fact, the steering resistance imposed by the yaw dampers on the bogies during the low-speed negotiation of sharp curves increases the guiding contact forces with negative effects on both running safety and wheel/rail wear. This paper introduces a Switchable Yaw Damper (SYD), a semi-active on/off device designed to overcome the design tradeoff of yaw dampers by means of an additional controlled valve implemented to reduce the damping force during curve negotiation. The SYD has been prototyped, experimentally characterized, and modelled. To quantify the SYD influence on the curving performances of a rail vehicle, a multibody model has been introduced to simulate a set of real operating conditions. The curving performances of the vehicle with SYD have been compared with the ones obtained with standard yaw dampers. The comparison shows that the SYD damper technology is a simple and robust way to overcome the tradeoff that limits the design of standard yaw dampers.