Study of the possible relationships between tramway front-end geometry and pedestrian injury risk

Abstract

The aim of this paper is to report on the possible relationships between tramway front end geometry and pedestrian injury risk over a wide range of possible tramway shapes. Methods: To study the effect of tramway front-end shape on pedestrian injury metrics, accidents were simulated using a custom parametrized model of tramway front-end and pedestrian models available with the MADYMO multibody solver. The approach was automated, allowing the systematic exploration of tramway shapes in conjunction with four pedestrian sizes (e.g. 50 th percentile male or M50). Results: A total of 8,840 simulations were run, showing that the injury risk is more important for the head than for the other body regions (thorax and lower extremities). The head of the M50 impacted the windshield of the tramway in most of the configurations. Two antagonist mechanisms affecting impact velocity of the head and corresponding HIC values were observed. The first is a trunk rotation resulting from an engagement of the lower body that can contribute to an increase of the head velocity in the direction of the tram. The second is the loading of the shoulder that can accelerate the upper trunk and head away from the windshield, resulting in lower impact velocities. Groups of design were defined based on two main parameters (windshield height and offset), some of which seem more beneficial than others for tramway design. The pedestrian size and tramway velocity (30km/h vs. 20km/h) also affected the results. Conclusions: When considering only the frontend shape, the best strategy to limit the risk of head injury due to the contact with the stiff windshield seems to be to promote the mechanism involving shoulder loading. As body regions engaged vary with the pedestrian size, none of the groups of designs performed equally well for all pedestrian sizes. The best compromise seems achieved with a combination of a large windscreen offset and a high windscreen. Conversely, particularly unfavorable configurations are observed for low windshield heights, especially with a large offset. Beyond the frontend shape, considering the stiffness of the current windshields and the high injury risks predicted for 30km/h, the stiffness of the windshield should be considered in the future for further gains in pedestrian safety.

Tram to Pedestrian Collisions—Priorities and Potentials

“…However, injury severity for pedestrians is higher in tram-pedestrian accidents than in accidents with other motor vehicles. This particular higher injury risk has been documented in a number of studies, such as Hedelin et al, 2002;Margaritis, 2007;Naznin et al, 2016b;Chevalier et al, 2019, andGaca andFranek, 2021.…”

“…In general, the severity of tram-pedestrian accidents is primarily affected by vehicle related factors, especially by the mass difference between a tram and a human (a tram vehicle can weigh up to 50 tonnes) and ergonomics and stiffness of the vehicle's front (Hedelin et al, 1996;Grzebieta and Rechnitzer, 2000;Margaritis, 2007;COST, 2015;Gaca and Franek, 2021). A simulation study by Chevalier et al, 2019 on the effects on pedestrian injury by tram front-end shape, showed that the injury risk is more severe for the head than any other body region. Špirk et al (2021) stated that the most prominent part of the tram front-end responsible for the level of head injury is the windshield.…”

Assessment of Pedestrians’ Head and Lower Limb Injuries in Tram–Pedestrian Collisions

“…The ground was represented using *RIGIDWALL in the LS-DYNA software, and a friction coefficient of 0.7 between the pedestrian and the ground was assigned [37]. The contact between the tram and the pedestrian was modeled using *CONTANT_SURFACE_TO_SURFACE, with the friction coefficient set to 0.35 [17]. The normal walking speed of pedestrians is 1.4 m/s [40]; the pedestrian model speed was set to 1.4 m/s using *INITIAL_VELOCITY.…”

“…They discovered that pedestrians' knee injuries were primarily caused by tram fenders and were challenging to avoid. Chevalier et al [17] investigated the influence of tram front-end shape on pedestrians' head injuries, employing a customized parameterized front-end simplification model. The study found that the risk of head injury was more significant compared with other body regions, and a combination of a large windscreen offset and a high windscreen reduced the likelihood of head injuries to pedestrians.…”

“…All of the aforementioned studies indicate that pedestrian dynamics are obviously affected by the interaction between the lower extremities and the front end of the tram. Direct collisions between the human head and the tram windshield often result in major traumas [17,22]. However, most of these studies were conducted on traditional older trams.…”