Investigations on tram-pedestrian impacts by application of virtual testing with human body models

Background: In Austria around 100 trams are involved in accidents with pedestrians every year. Since the service lives of trams are very high, the probabilities are also high that each tram on the network will be involved in an accident of this kind at least once, highlighting the need of protective designs of tram fronts. However, due to lack of studies in this area, this is still a challenging task. Purpose: The aim of this study is to show the applicability and the usability of virtual testing involving HBMs in tram front design studies to improve passive safety in general. Methodology: In this study, the impact of pedestrians with a tram was investigated using a generic tram front model in a basic version and a conceptually improved version, respectively, and detailed finite element human body models (HBM). To consider gender-differences and to avoid designs that unintentionally favour only particular groups of the population, the study simulations were carried out with a male and a female 50th percentile finite element human body model (VIVA+). The risk for head, chest, femur and tibia injuries were analysed as the simulation result, since these body areas were identified based on field data to be most relevant in accidents involving pedestrians and trams. Collision scenarios are evaluated for a wide parameter variation in impact location and speed, respectively. Findings: The results show a reduction in head injury risk for both the female and the male HBM at different speeds and impact locations for impact with the enhanced version of the tram front. Depending on the gender of the HBM, the considered improvement shows different effects for each body region, with a greater reduction in the likelihood of head injury for the female model, and a greater reduction in the likelihood of thoracic injury for the male model. These differences are due to the considered anthropomorphic variations. A reduction for the risk of femur injuries can be achieved in all cases using the modified tram front. The study showcases the application of detailed human body models for tram pedestrian impact analyses in the context of pedestrian safety and in particular for tram front improvements. It was shown that even a minor modification of the tram front with softer front skirt attachments leads to remarkable benefits with respect to injury criteria in all investigated crash scenarios. The presented research goes beyond current technical recommendations and shows the benefit of virtual testing including HBMs and considering a wide variety of impact speeds, anthropometries and injury assessments, respectively.