Study of the possible relationships between tramway front-end geometry and pedestrian injury risk
Objectives: The aim of this article 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 parameterized 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 4 pedestrian sizes (e.g., 50th 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 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 head injury criterion (HIC) values were observed. The first is a trunk rotation resulting from an engagement of the lower body that can contribute to an increase in head velocity in the direction of the tram. The second is the loading of the shoulder, which can accelerate the upper trunk and head away from the windshield, resulting in lower impact velocities. Groups of design were defined based on 2 main parameters (windshield height and offset), some of which seem more beneficial than others for tramway design. The pedestrian size and tramway velocity (30 vs. 20 km/h) also affected the results.
Conclusions: When considering only the front-end shape, the best strategy to limit the risk of head injury due to contact with the stiff windshield seems to be to promote the mechanism involving shoulder loading. Because body regions engaged vary with the pedestrian size, none of the groups of designs performed equally well for all pedestrian sizes. The best compromise is 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 front-end shape, considering the stiffness of the current windshields and the high injury risks predicted for 30 km/h, the stiffness of the windshield should be considered in the future for further gains in pedestrian safety.