Every year, many deaths, injuries and much economic loss due to falling rocks and boulders occur to the people who live in and pass through mountainous regions worldwide. Closed transportation corridors and damage to infrastructures, like rock sheds, due to rock falls, are common phenomena in some countries, especially during rainfall or earthquake. Realistic simulation of rock falls, along with defining their most vulnerable fall trajectories, can result in providing mitigation measures in the right places with the least cost. While many numerical approaches have been developed to predict the trajectory of falling rocks, none of them consider the interaction between the blocks of falling objects. In this paper, a common discrete element software (i.e., Working Model 3D) has been employed as a new tool to model rock fall. The interaction between falling masses, i.e., the impact between falling rock blocks, is considered. The results are compared to those obtained from traditional rock fall simulations. While the recent approach gives a more realistic result, its drawback is the enormous time needed to perform calculations, i.e. more than ten to a hundred fold, depending on the number of falling objects involved. The results show that existing simulation techniques give a lower bound for the hazard zone scattering and, consequently, the measuring structures will not be very efficient. On the other hand, designers should over-design to cover unseen hazard zones, which lead to heavy project costs.