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During traction and braking of trains, substantial longitudinal dynamic forces might occur in couplers. The method of modeling these forces for two different electric multiple units (EMUs) is presented in this study. Computer simulations were carried out for EMUs consisted of independent vehicles, each of which rests on two bogies. Simulations were also carried out for EMUs with Jacobs bogies, which support bodies of two adjacent carriages. The dynamic modeling of vibration train protection systems includes nonlinearities.