External Biofidelity Evaluation of Pedestrian Leg-Form Impactors

Current state-of-the-art vehicles implement pedestrian protection features that rely on pedestrian detection sensors and algorithms to trigger when impacting a pedestrian. During the development phase, the vehicle must “learn” to discriminate pedestrians from the rest of potential impacting objects. Part of the training data used in this process is often obtained in physical tests utilizing legform impactors whose external biofidelity is still to be evaluated. This study uses THUMS as a reference to assess the external biofidelity of the most commonly used impactors (Flex-PLI, PDI-1 and PDI-2). This biofidelity assessment was performed by finite element simulation measuring the bumper beam forces exerted by each surrogate on a sedan and a SUV. The bumper beam was divided in 50 mm sections to capture the force distribution in both vehicles. This study, unlike most of the pedestrian-related literature, examines different impact locations and velocities. The results show how the Flex-PLI and the PDI-1 exert greater forces on the bumper beam than the THUMS, while the PDI-2 produced bumper beam forces similar to the THUMS. The PDI-2 is often used to represent the Hardest To Detect (HTD) surrogate in pedestrian detection assessments. These results indicate that the PDI-2 produces bumper forces similar to what would be produced by a 50th percentile male, suggesting that an alternative means may be needed to evaluate HTD scenarios. These results also suggest that the Flex-PLI or the PDI-1 are likely to produce bumper forces greater than would be produced by contact with a human. Studies with different vehicle and pedestrian sizes would be needed to fully understand the impactors’ performance.