In this work the multibody (MB) approach has been used to study the structural behaviour of a M3 bus in a rollover accident, to evaluate the structure resistance and passenger injury risks. This research is part of the ECBOS project (Enhanced Coach and Bus Occupant Safety), granted by the European Union.

The interest was focused on the effect of a rollover accident over the structure and the passengers. For what concerns the rollover of a bus, in Europe the regulation for safety approval is the ECE Regulation 66 [1]. This regulation prescribes a test to be chosen between four of different kind:​ a complete bus rollover test, a bay section rollover test, a pendulum test and a numerical simulation of a rollover. The choice between these tests is completely up to the coach manufacturer. It is important to underline that in all these tests the presence of passengers is not considered.

The effect of the mass of the occupants over the superstructure and the injury risk for passengers in a rollover accident was evaluated considering different configurations. Only a bay section has been modelled:​ in a rollover event, with rotation axis parallel to the longitudinal bus axis, the behaviour of the bay section is well representative of the whole structure. To generate the virtual model of the bay section, the plastic hinge concept has been adopted by using generalized spring elements to represent the constitutive characteristics of localized plastic deformations. The program chosen to carry out the simulations is MADYMO, a MB-FE software developed by TNO, which has a complete library of virtual dummies.

The numerical analysis has given prominence to the inadequacy of the actual European regulation (ECE66), concerning passive safety. The mass increment due to presence of the passengers affects significantly the deformation of the superstructure and the absence of any prescription of restrain systems does not permit to protect the passengers against very serious or fatal injuries.