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This paper presents an application of multibody dynamics with unilateral contact to model the friction wedge interaction with the bolster and the side frame. The new friction wedge model is a three-dimensional, dynamic, stand-alone model of a bolster–friction wedge–side frame assembly. It allows the wedge four degrees of freedom: vertical displacement; longitudinal (between the bolster and the side frame) displacement; toe in and toe out; and yaw (rotation about the vertical axis). The dedicated train modeling software NUCARS (Transportation Technology Center, Inc., Pueblo, Colo.) has been used to run simulations with similar inputs and to compare—when possible—the results with those obtained from the new stand-alone MATLAB (MathWorks, Natick, Mass.) friction wedge model. The stand-alone model shows improvement in capturing the transient dynamics of the wedge better. Also, it can predict not only normal forces going into the side frame and bolster, but also the associated moments. Significant simulation results are presented and the main differences between the current NUCARS model and the new stand-alone MATLAB models are highlighted. [ABSTRACT FROM AUTHOR]