The aggressivity of trucks to other road users in daily traffic is widely known. The incompatibility is the origin mostly of serious and fatal injuries. Much harm can be anticipated by preventing for underride. Most serious and fatal injuries is inflicted to occupants of passenger cars in frontal collisions with trucks. An underrun protection device helps to address the energy absorbing structure of the passenger car and thus reduces excessive deformation of the occupant compartment. Research on front underrun protection (FUP) for trucks by means of full scale testing, and especially on energy absorbing systems, is extensive and time consuming. Therefore simulation tools are applied in the early stage of the design process in order to obtain the basic parameters for later testing. In this presentation it is shown how MADYMO was used with combined multibody/finite element models of a truck with different types of FUP and a car in order to evaluate different FUP systems in car-to-truck frontal collisions.